Surface acoustic wave apparatus and manufacturing method therefor

ABSTRACT

In a manufacturing method for a SAW apparatus a first insulating layer is formed on the entire surface of a piezoelectric LiTaO 3  substrate. By using a resist pattern used for forming an IDT electrode, the first insulating layer in which the IDT electrode is to be formed is removed. An electrode film made of a metal having a density higher than Al or an alloy primarily including such a metal is disposed in the area in which the first insulating layer is removed so as to form the IDT electrode. The resist pattern remaining on the first insulating layer is removed. A second insulating layer is formed to cover the first insulating layer and the IDT electrode.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a surface acoustic wave (SAW)apparatus used in, for example, resonators and bandpass filters and alsoto a manufacturing method for this type of SAW apparatus. Morespecifically, the invention relates to a SAW apparatus having astructure in which an insulating layer is disposed to cover aninterdigital (IDT) electrode and also to a manufacturing method for thistype of SAW apparatus.

[0003] 2. Description of the Related Art

[0004] DPX or RF filters used in mobile communication systems need tosatisfy wide-band and good temperature characteristics. In known SAWapparatuses used in DPX or RF filters, piezoelectric substrates formedof 36°-50°-rotated Y-plate X-propagating LiTaO₃ are used. This type ofpiezoelectric substrate has a temperature coefficient of frequency (TCF)of about −40 to −30 ppm/° C. In order to improve the temperaturecharacteristic, it is known that a SiO₂ film having a positive TCF isformed to cover an IDT electrode on a piezoelectric substrate. Anexample of a manufacturing method for this type of SAW apparatus isshown in FIGS. 109A through 109D.

[0005] As shown in FIG. 109A, a resist pattern 52 is formed on apiezoelectric substrate 51 except for an area in which an IDT electrodeis to be formed. Then, as shown in FIG. 109B, an electrode film 53,which serves as an IDT electrode, is formed on the entire surface of thepiezoelectric substrate 51. Subsequently, by using a resist stripper,the resist pattern 52 and a metallic film attached to the resist pattern52 are removed, thereby forming an IDT electrode 53A, as shown in FIG.109C. Then, as shown in FIG. 109D, a SiO₂ film 54 is formed to cover theIDT electrode 53A.

[0006] For achieving an object other than the improvement of the TCF,another manufacturing method for a SAW apparatus in which an insulatingor non-conductive protective film is formed to cover an IDT electrode isdisclosed in Japanese Unexamined Patent Application Publication No11-186866. FIG. 110 is a schematic sectional view illustrating a SAWapparatus 61 taught in JP 11-186866. In the SAW apparatus 61, an IDTelectrode 63 made of Al or an alloy primarily including Al is disposedon an insulating substrate 62. In an area other than an area in whichthe IDT electrode 63 is disposed, an insulating or non-conductiveinter-electrode-finger film 64 is disposed. An insulating ornon-conductive protective film 65 is also disposed to cover the IDTelectrode 63 and the inter-electrode-finger film 64. In the SAWapparatus 61 disclosed in JP 11-186866, the inter-electrode-finger film64 and the protective film 65 are made of an insulating material, forexample, SiO₂, or a non-conductive material, for example, silicone. Byforming the inter-electrode-finger film 64, discharging between theelectrode fingers caused by a pyroelectric property unique to thepiezoelectric substrate 62 can be suppressed.

[0007] Japanese Unexamined Patent Application Publication No. 61-136312teaches the following type of one-port SAW resonator. An electrode madeof a metal, such as aluminum or gold, is disposed on a piezoelectricsubstrate made of quartz or lithium niobate. Then, after a SiO₂ film isformed, it is planarized. In this type of resonator, good resonancecharacteristics can be achieved by planarizing the SiO₂ film.

[0008] As shown in FIGS. 109A through 109D, in the manufacturing methodfor SAW apparatuses in which the SiO₂ film 54 is formed for improvingthe TCF, the height of the SiO₂ film 54 is different between a portionwith the IDT electrode 53A and a portion without the IDT electrode 53A.Because of the differences in the height of the SiO₂ film 54, theinsertion loss is increased. These differences in height increase as thethickness of the IDT electrode 53A becomes larger. Thus, the thicknessof the IDT electrode 53A cannot be increased.

[0009] In the SAW apparatus 61 taught in JP 11-186866, after theinter-electrode-finger film 64 is formed between the electrode fingersof the IDT electrode 63, the protective film 65 is formed. Accordingly,the height of the protective film 65 is uniform, unlike the SAWapparatus shown in FIGS. 109A through 109D.

[0010] In this configuration, because the inter-electrode-finger film 64is formed in contact with the IDT electrode 63 which is made of Al or analloy primarily including Al, a sufficient reflection coefficient is notobtained in the IDT electrode 63, thereby causing the generation ofripples in the resonance characteristics.

[0011] Also, in the manufacturing method taught in JP 11-186866, theresist formed on the inter-electrode-finger film 64 must be removed by aresist stripper before forming the protective film 65. In this case, theIDT electrode 63 may be disadvantageously eroded by the resist stripper.This requires the use of erosion-resistant metal for the IDT electrode63, thereby decreasing flexibility in selecting the type of metal usedin the IDT electrode 63.

[0012] In the one-port SAW resonator taught in JP 61-136312, quartz orlithium niobate is used for the piezoelectric substrate, and theelectrode is made of aluminum or gold. In JP 61-136312, only theembodiment in which the electrode is made of Al and is disposed on aquartz substrate is taught, and no specific reference is made to a SAWapparatus using a substrate made of another type of material or anelectrode made of another type of metal.

[0013] JP 61-136312 teaches that superior resonance characteristics areachieved by planarizing the SiO₂ film. Then, in order to obtain awide-band filter, the present inventors formed a one-port SAW resonatorhaving a structure similar to the structure taught in JP 61-136312,except that a LiTaO₃ substrate having a large electromechanical couplingcoefficient was used as the piezoelectric substrate. The presentinventors then examined the characteristics of the one-port SAW filter.

[0014] More specifically, an Al electrode was formed on the LiTaO₃substrate, and then, a SiO₂ film was formed and the surface of the SiO₂film was planarized. However, a considerable deterioration in thecharacteristics after the formation of the SiO₂ film was observed, andthe present inventors found that this SAW resonator cannot be put topractical use.

[0015] By using a LiTaO₃ substrate or a LiNbO₃ substrate having a largerelectromechanical coupling coefficient than quartz, the fractionalbandwidth is increased considerably. However, the present inventorsfound that, after the formation of an Al electrode on a LiTaO₃ substrateand after the formation of a SiO₂ film, the reflection coefficient wassharply decreased to about 0.02, as shown in FIGS. 2 and 3, caused bythe planarization of the SiO₂ film. FIGS. 2 and 3 illustrate therelationship between the reflection coefficient and the thickness H/λ ofthe IDT electrodes when the IDTs are made of Al, Au, Pt, Cu, and Ag andthe SiO₂ film were formed on a LiTaO₃ substrate having Euler angles (0°,126°, 0°). The solid lines in FIGS. 2 and 3 represent a relationshipbetween the reflection coefficient and the thickness H/λ of the IDTelectrodes when the surface of the SiO₂ film was not planarized. Thebroken lines indicate a relationship between the reflection coefficientand the thickness H/λ of the IDT electrodes when the surface of the SiO₂film was planarized.

[0016]FIGS. 2 and 3 show that, when the Al electrode was used, thereflection coefficient is decreased considerably to about 0.02 by theplanarization of the surface of the SiO₂ film, regardless of thethickness of the IDT electrode. Accordingly, a sufficient stop bandcannot be achieved, causing the generation of sharp ripples in thevicinity of the antiresonant frequency.

[0017] It is known that the reflection coefficient becomes larger as thethickness of an electrode is increased. As is seen from FIGS. 2 and 3,the reflection coefficient is not increased as the thickness of the Alelectrode is increased when the surface of the SiO₂ film was planarized.

[0018] In contrast, as is seen from FIG. 2, the reflection coefficientis increased as the thickness of the Au or Pt electrode is increasedeven when the surface of the SiO₂ film was planarized.

SUMMARY OF THE INVENTION

[0019] Based on the above-described discovery and to overcome theproblems described above, preferred embodiments of the present inventionprovide a SAW apparatus in which an insulating layer is formed betweenelectrode fingers of an IDT electrode and on the IDT electrode in orderto achieve a sufficiently large reflection coefficient of the IDTelectrode and in order to suppress characteristic deterioration causedby ripples generated in the resonance characteristics, which results insuperior resonance characteristics and superior filter characteristics.Another preferred embodiment of the present invention provides amanufacturing method for such a novel SAW apparatus.

[0020] Another preferred embodiment of the present invention provides aSAW apparatus that has superior characteristics, for example, asufficiently large reflection coefficient of an IDT electrode and a highdegree of flexibility in selecting the type of material forming the IDTelectrode so as to decrease the possibility of erosion of the IDTelectrode, and a manufacturing method for such a novel SAW apparatus.

[0021] Yet another preferred embodiment of the present inventionprovides a SAW apparatus that has superior characteristics, for example,a sufficiently large reflection coefficient of an IDT electrode, adecreased possibility of erosion of the IDT electrode, and a superiortemperature coefficient of frequency (TCF), and a manufacturing methodfor such a novel SAW apparatus.

[0022] According to a first preferred embodiment of the presentinvention, a SAW apparatus includes a piezoelectric substrate, at leastone electrode disposed on the piezoelectric substrate and including atleast one of a metal having a density higher than Al and an alloyprimarily including a metal having a density higher than Al, a firstinsulating layer provided on the piezoelectric substrate in an areaother than an area in which the electrode is provided such that thefirst insulating layer has substantially the same thickness as thethickness of the electrode, and a second insulating layer arranged tocover the electrode and the first insulating layer In the firstpreferred embodiment of the present invention, the density of theelectrode is about 1.5 times or greater than the density of the firstinsulating layer.

[0023] With this configuration, a sufficient reflection coefficient ofthe electrode can be obtained. Thus, ripples generated in the resonancecharacteristic or the antiresonance characteristic are shifted outsidethe pass band, and the ripples themselves are suppressed. The TCF isalso improved. Additionally, because the height of the electrode issubstantially the same as that of the first insulating layer, theinsertion loss can be minimized.

[0024] According to a second preferred embodiment of the presentinvention, a SAW apparatus includes a piezoelectric substrate, at leastone electrode provided on the piezoelectric substrate, a protectivemetal film provided on the electrode and including a metal or an alloyhaving higher erosion-resistant characteristics than the metal or thealloy forming the electrode, a first insulating layer arranged on thepiezoelectric substrate in an area other than an area in which theelectrode is arranged so that the thickness of the first insulatinglayer is substantially the same as the total thickness of the electrodeand the protective metal film, and a second insulating layer provided tocover the protective metal film and the first insulating layer.

[0025] With this configuration, because the electrode is covered withthe protective metal film and the first insulating layer, the erosion ofthe electrode by a resist stripper when removing a resist pattern issuppressed.

[0026] In the second preferred embodiment of present invention, theaverage density of the laminated structure of the electrode and theprotective metal film may be about 1.5 times or greater than the densityof the first insulating layer. With this arrangement, unwanted ripplesappearing in the resonance characteristic or the filter characteristicare shifted outside the pass band.

[0027] In the first or second preferred embodiment of the presentinvention, the first and second insulating layers may include SiO₂.Thus, a SAW apparatus having an improved TCF is provided.

[0028] In the first or second preferred embodiment of the presentinvention, the reflection of a SAW may be preferably utilized. Thestructure of a SAW apparatus utilizing the reflection of a SAW is notparticularly restricted. and An end-surface-reflection-type SAWapparatus utilizing the reflection of two opposing side surfaces of apiezoelectric substrate or a SAW apparatus provided with reflectorsdisposed to sandwich an electrode therebetween in the SAW propagatingdirection may be used.

[0029] The SAW apparatus of the first or second preferred embodiment ofthe present invention can be used in various types of SAW resonators andSAW filters. The SAW resonator may be a one-port resonator or a two-portresonator, and the SAW filter may be a two-port resonator filter, aladder filter, or a lattice filter.

[0030] In the first or second preferred embodiment of the presentinvention, the electrode may be an IDT electrode. The IDT electrode maybe a unidirectional electrode in which the insertion loss can bereduced. Alternatively, the electrode may be a reflector.

[0031] In the first or second preferred embodiment of the presentinvention, the piezoelectric substrate may be a LiTaO₃ substrate havingEuler angles of about (0±3°, 104°-140°, 0±3°), the first and secondinsulating layers may include a SiO₂ film, the normalized thickness Hs/λmay range from about 0.03 to about 0.45 where Hs is a total thickness ofthe SiO₂ film of the first and second insulating layers and λ is thewavelength of a SAW, and the normalized thickness H/λ of the electrodemay satisfy the following equation (1):

0.005≦H/λ≦0.00025×

²−0.01056×

+0.16473  Equation (1)

[0032] where H indicates the thickness of the electrode and Q representsthe average density of the electrode.

[0033] Au, Ag, Cu, W, Ta, Pt, Ni, or Mo may be used in forming theelectrode.

[0034] In preferred embodiments of the present invention, the electrodemay be made of one of the above-described metals or an alloy primarilyincluding such a metal, or formed of a laminated film including aprimary metallic film made of one of the above-described metals or analloy including one of the above-described metals. According to the typeof metal, the normalized thickness H/λ of the electrode, the Eulerangles of the piezoelectric substrate, and the total normalizedthickness Hs/λ of the first and second SiO₂ insulating layers aredefined to be within specific ranges, thereby improving theelectromechanical coupling coefficient, the reflection coefficient, andthe TCF. The attenuation constant can also be reduced.

[0035] According to a third preferred embodiment of the presentinvention, a method of manufacturing the SAW apparatus according to thefirst preferred embodiment of the present invention includes preparing apiezoelectric substrate, forming a first insulating layer on theentirety of one surface of the piezoelectric substrate, removing, byusing a resist pattern for forming an electrode pattern including atleast one electrode, the at least a portion of the first insulatinglayer in an area in which the electrode is to be formed, and maintaininga laminated structure of the first insulating layer and the resistpattern in an area other than the area in which the electrode is to beformed; forming the at least one electrode by forming an electrode filmincluding at least one of a metal having a density higher than Al, analloy including a metal having a density higher than Al in an area ofthe portion of the first insulating layer which was removed so that thethickness of the electrode film becomes substantially the same as thethickness of the first insulating layer, removing the resist pattern onthe first insulating layer, and forming a second insulating layer tocover the first insulating layer and the electrode.

[0036] With this configuration, because the second insulating layer isformed to cover the first insulating layer and the electrode, there issubstantially no difference in the height of the top surface of thesecond insulating layer, thereby reducing the insertion loss.Additionally, because the electrode is made of a metal or an alloyhaving a density higher than Al, the reflection coefficient of theelectrode can be improved, thereby suppressing characteristicdeterioration caused by unwanted ripples.

[0037] In the manufacturing method of the third preferred embodiment ofthe present invention, the density of the metal or the alloy forming theelectrode may be about 1.5 times or greater than that of the firstinsulating layer. With this arrangement, unwanted ripples appearing inthe resonance characteristic or the filter characteristic are shiftedoutside the pass band.

[0038] According to a fourth preferred embodiment of the presentinvention, a method of manufacturing the SAW apparatus of the secondpreferred embodiment of the present invention includes preparing apiezoelectric substrate, forming a first insulating layer on theentirety of one surface of the piezoelectric substrate, removing aportion of the first insulating layer by using a resist pattern,maintaining a laminated structure of the first insulating layer and theresist pattern, forming at least one electrode by forming a metal or analloy in an area of the portion of the first insulating layer which wasremoved, forming a protective metal film made of a metal or an alloyhaving higher erosion-resistant characteristics than the metal or thealloy of the at least one electrode on the entire surface of the atleast one electrode so that the height of the protective metal filmbecomes substantially the same as the height of the first insulatinglayer, removing the resist pattern on the first insulating layer, andforming a second insulating layer to cover the protective metal filmformed on the electrode and the first insulating layer.

[0039] With this configuration, in the step of removing the resistpattern, because the side surfaces of the electrode are covered with thefirst insulating layer and the top surface is covered with theprotective metal film, the erosion of the electrode can be suppressed.

[0040] In the fourth preferred embodiment of the present invention, themetal or the alloy forming the electrode and the metal or the alloyforming the protective metal film may be selected so that the averagedensity of the laminated structure of the electrode and the protectivemetal film is about 1.5 times or greater than the density of the firstinsulating layer. With this arrangement, unwanted ripples appearing inthe resonance characteristic or the filter characteristic are shiftedoutside the pass band.

[0041] According to a fifth preferred embodiment of the presentinvention, a method of manufacturing a SAW apparatus includes preparinga piezoelectric substrate, forming an electrode on the piezoelectricsubstrate, forming an insulating layer to cover the electrode, andplanarizing a difference of the height of the insulating layer.Accordingly, a characteristic deterioration caused by the differences inthe height of the top surface of the insulating layer can be suppressed.

[0042] In the fifth preferred embodiment of the present invention, theplanarizing step may preferably be performed by an etch back process, areverse sputtering process, or a polishing process.

[0043] Other features, elements, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments thereof with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044]FIGS. 1A through 1G are partially cut sectional viewsschematically illustrating a manufacturing method for a SAW apparatusaccording to a first preferred embodiment of the present invention;

[0045]FIG. 2 illustrates the relationship between the reflectioncoefficient and the electrode thickness when the surface of a SiO₂ filmis planarized and when the surface of the SiO₂ film is not planarized ofa one-port SAW resonator in which IDT electrodes made of aluminum (Al),Gold (Au), or platinum (Pt) having various thickness values and the SiO₂film having a normalized thickness of about 0.2 are formed on a LiTaO₃substrate having Euler angles (0°, 126°, 0°);

[0046]FIG. 3 illustrates the relationship between the reflectioncoefficient and the electrode thickness when the surface of a SiO₂ filmis planarized and when the surface of the SiO₂ film is not planarized ofa one-port SAW resonator in which IDT electrodes made of Al, copper(Cu), or silver (Ag) having various thickness values and the SiO₂ filmhaving a normalized thickness of about 0.2 are formed on a LiTaO₃substrate having Euler angles (0°, 126°, 0°);

[0047]FIG. 4 illustrates the impedance and the phase with respect to thefrequency when the SiO₂ film of a SAW resonator formed by amanufacturing method of a first comparative example was changed;

[0048]FIG. 5 illustrates the relationship between the Figure of Merit(MF) of the resonator and the thickness of the SiO₂ film of the SAWresonator of the first comparative example;

[0049]FIG. 6 is a schematic plan view illustrating a one-port SAWresonator obtained by the manufacturing method shown in FIGS. 1A through1G;

[0050]FIG. 7 illustrates the impedance and the phase with respect to thefrequency when the SiO₂ film of the SAW resonator obtained by themanufacturing method of the first preferred embodiment of the presentinvention was changed;

[0051]FIG. 8 illustrates the relationship of γ of the SAW resonatorobtained by the manufacturing method of the first preferred embodimentof the present invention and that of the first comparative example tothe thickness of the SiO₂ film;

[0052]FIG. 9 illustrates the relationship of the MF of the SAW resonatorobtained by the manufacturing method of the first preferred embodimentof the present invention and that of the first comparative example tothe thickness of the SiO₂ film;

[0053]FIG. 10 illustrates the relationship between the temperaturecoefficient of frequency (TCF) and the thickness of the SiO₂ film of theSAW resonator obtained by the manufacturing method of the firstpreferred embodiment of the present invention and that of the firstcomparative example;

[0054]FIG. 11 illustrates the impedance and the phase with respect tothe frequency of a SAW resonator with a SiO₂ film and a SAW resonatorwithout a SiO₂ film manufactured by a second comparative example;

[0055]FIGS. 12A through 12E illustrate the impedance with respect to thefrequency when the ratio of the average density of the IDT electrode andthe protective metal film to the density of the first insulating layerwas changed;

[0056]FIG. 13 illustrates a change in the electromechanical couplingcoefficient when IDT electrodes made of various metals having variousthickness values were formed on a LiTaO₃ substrate having Euler angles(0°, 126°, 0°);

[0057]FIG. 14 illustrates the relationship of the range of the electrodethickness that exhibits greater electromechanical coupling coefficientsthan Al to the density of the corresponding electrode when IDTs made ofvarious metals were formed on a LiTaO₃ substrate;

[0058]FIG. 15 is a plan view illustrating a SAW apparatus according to asecond preferred embodiment of the present invention;

[0059]FIG. 16 illustrates the relationship between the electromechanicalcoupling coefficient and the normalized thickness of IDTs when the IDTsmade of Au, Ta, Ag, Cr, W, Cu, Zn, Mo, Ni, and Al were formed on a36°-rotated Y-plate X-propagating LiTaO₃ substrate having Euler angles(0°, 126°, 0°);

[0060]FIG. 17 illustrates the relationship between the reflectioncoefficient of a single electrode finger of IDTs made of variouselectrode materials on a 36°-rotated Y-plate X-propagating LiTaO₃substrate having Euler angles (0°, 126°, 0°) and the thickness of theIDTs;

[0061]FIG. 18 illustrates the relationship between the attenuationconstant α and the normalized thickness of IDTs when the IDTs made ofAu, Ta, Ag, Cr, W, Cu, Zn, Mo, Ni, and Al were formed on a 36°-rotatedY-plate X-propagating LiTaO₃ substrate having Euler angles (0°, 126°,0°);

[0062]FIG. 19 illustrates a change in the TCF with respect to thenormalized thickness of a SiO₂ film when an Au IDT having a normalizedthickness of 0.02 was formed on a 36°-rotated Y-plate X-propagatingLiTaO₃ substrate having Euler angles (0°, 126°, 0°);

[0063]FIG. 20 illustrates a change in the attenuation constant α withrespect to the normalized thickness of a SiO₂ film when Au IDTs havingvarious thickness values were formed on a 36°-rotated Y-plateX-propagating LiTaO₃ substrate having Euler angles (0°, 126°, 0°);

[0064]FIG. 21 illustrates a change in the attenuation constant α withrespect to the normalized thickness of a SiO₂ film when Au IDTs havingvarious thickness values were formed on a 38°-rotated Y-plateX-propagating LiTaO₃ substrate having Euler angles (0°, 128°, 0°);

[0065]FIG. 22 illustrates the attenuation-vs.-frequency of the SAWapparatus of the first preferred embodiment of the present inventionbefore and after a SiO₂ film was formed;

[0066]FIG. 23 illustrates a change in the acoustic velocity of a leakySAW with respect to the thickness of an Au IDT when the Au IDT and SiO₂films having various thickness values were formed on a 36°-rotatedY-plate X-propagating LiTaO₃ substrate having Euler angles (0°, 126°,0°);

[0067]FIG. 24 illustrates a change in the acoustic velocity of a leakySAW with respect to the thickness of a SiO₂ film when Au IDTs havingvarious thickness values and the SiO₂ film were formed on a 36°-rotatedY-plate X-propagating LiTaO₃ substrate having Euler angles (0°, 126°,0°);

[0068]FIG. 25 illustrates a change in the electromechanical couplingcoefficient with respect to Θ of Euler angles (0°, Θ, 0°) when thenormalized thickness of an Au IDT and the normalized thickness of a SiO₂film were changed;

[0069]FIG. 26 illustrates a change in the Q factor with respect to e ofEuler angles (0°, Θ, 0°) when the normalized thickness of a SiO₂ filmwas changed;

[0070]FIGS. 27A through 27C are schematic sectional views illustrating aSAW apparatus of a modified example of preferred embodiments of thepresent invention provided with a contact layer;

[0071]FIG. 28 illustrates a change in the attenuation constant α withrespect to Θ of Euler angles (0°, Θ, 0°) when the normalized thicknessof a SiO₂ film was about 0.1 and when Au electrodes having variousthickness values were formed;

[0072]FIG. 29 illustrates a change in the attenuation constant α withrespect to Θ of Euler angles (0°, Θ, 0°) when the normalized thicknessof a SiO₂ film was about 0.15 and when Au electrodes having variousthickness values were formed;

[0073]FIG. 30 illustrates a change in the attenuation constant α withrespect to Θ of Euler angles (0°, Θ, 0°) when the normalized thicknessof a SiO₂ film was about 0.12 and when Au electrodes having variousthickness values are formed;

[0074]FIG. 31 illustrates a change in the attenuation constant α withrespect to Θ of Euler angles (0°, Θ, 0°) when the normalized thicknessof a SiO₂ film was about 0.25 and when Au electrodes having variousthickness values were formed;

[0075]FIG. 32 illustrates a change in the attenuation constant α withrespect to Θ of Euler angles (0°, Θ, 0°) when the normalized thicknessof a SiO₂ film was about 0.3 and when Au electrodes having variousthickness values were formed;

[0076]FIG. 33 illustrates a change in the attenuation constant α withrespect to Θ of Euler angles (0°, Θ, 0°) when the normalized thicknessof a SiO₂ film was about 0.35 and when Au electrodes having variousthickness values were formed;

[0077]FIG. 34 illustrates a change in the attenuation constant α withrespect to Θ of Euler angles (0°, Θ, 0°) when the normalized thicknessof a SiO₂ film was about 0.40 and when Au electrodes having variousthickness values were formed;

[0078]FIG. 35 illustrates a change in the attenuation constant α withrespect to Θ of Euler angles (0°, Θ, 0°) when the normalized thicknessof a SiO₂ film was about 0.45 and when Au electrodes having variousthickness values were formed;

[0079]FIG. 36 illustrates the relationship between the electromechanicalcoupling coefficient and the normalized thickness of an Ag electrodeformed on a LiTaO₃ substrate having Euler angles (0°, 126°, 0°)according to a third preferred embodiment of the present invention;

[0080]FIG. 37 illustrates the relationship between the TCF and thenormalized thickness of SiO₂ films formed on three LiTaO₃ substratehaving Euler angles (0°, 113°, 0°), (0°, 126°, 0°), and (0°, 129°, 0°);

[0081]FIG. 38 illustrates a change in the attenuation constant α when Agfilms having a normalized thickness of about 0.1 or smaller and SiO₂films having a normalized thickness of 0 to about 0.5 were formed on aLiTaO₃ substrate having Euler angles (0°, 120°, 0°);

[0082]FIG. 39 illustrates a change in the attenuation constant α when Agfilms having a normalized thickness of about 0.1 or smaller and SiO₂films having a normalized thickness of 0 to about 0.5 were formed on aLiTaO₃ substrate having Euler angles (0°, 140°, 0°);

[0083]FIG. 40 illustrates a change in the attenuation constant α when Agfilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.1 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0084]FIG. 41 illustrates a change in the attenuation constant α when Agfilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.15 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0085]FIG. 42 illustrates a change in the attenuation constant α when Agfilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.2 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0086]FIG. 43 illustrates a change in the attenuation constant α when Agfilms having a normalized thickness of about 01 or smaller and a SiO₂film having a normalized thickness of about 0.25 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0087]FIG. 44 illustrates a change in the attenuation constant α when Agfilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.3 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0088]FIG. 45 illustrates a change in the attenuation constant α when Agfilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.35 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0089]FIG. 46 illustrates a change in the attenuation constant α when Agfilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.4 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0090]FIG. 47 illustrates a change in the attenuation constant α when Agfilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.45 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0091]FIG. 48 illustrates a change in the attenuation constant α when Cufilms having a normalized thickness of about 0.1 or smaller and SiO₂films having a normalized thickness of 0 to about 0.5 were formed on aLiTaO₃ substrate having Euler angles (0°, 1200, 0°) according to afourth preferred embodiment of the present invention;

[0092]FIG. 49 illustrates a change in the attenuation constant α when Cufilms having a normalized thickness of about 0.1 or smaller and SiO₂films having a normalized thickness of 0 to about 0.5 were formed on aLiTaO₃ substrate having Euler angles (0°, 135°, 0°);

[0093]FIG. 50 illustrates a change in the attenuation constant α when Cufilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.1 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0094]FIG. 51 illustrates a change in the attenuation constant α when Cufilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.15 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0095]FIG. 52 illustrates a change in the attenuation constant α when Cufilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.2 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0096]FIG. 53 illustrates a change in the attenuation constant α when Cufilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.25 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0097]FIG. 54 illustrates a change in the attenuation constant α when Cufilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.3 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0098]FIG. 55 illustrates a change in the attenuation constant α when Cufilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.35 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0099]FIG. 56 illustrates a change in the attenuation constant α when Cufilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.4 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0100]FIG. 57 illustrates a change in the attenuation constant α when Cufilms having a normalized thickness of about 0.1 or smaller and a SiO₂film having a normalized thickness of about 0.45 were formed on a LiTaO₃substrate having Euler angles (0°, Θ, 0°);

[0101]FIG. 58 illustrates the relationship between the reflectioncoefficient per electrode finger of an Al electrode and that of a Cuelectrode and the normalized thickness of the corresponding electrodewhen the normalized thickness of a SiO₂ film was about 0.02;

[0102]FIG. 59 illustrates the relationship between θ_(min) that reducesthe attenuation constant α to 0 or minimizes the attenuation constant αand the normalized thickness of a SiO₂ film when the normalizedthickness of a Cu film was changed;

[0103]FIG. 60 illustrates a change in the attenuation constant α whenSiO₂ films having various thickness values and tungsten IDTs havingvarious thickness values were formed on a LiTaO₃ substrate (0°, 120°,0°) according to a fifth preferred embodiment of the present invention;

[0104]FIG. 61 illustrates a change in the attenuation constant α whenSiO₂ films having various thickness values and tungsten IDTs havingvarious thickness values were formed on a LiTaO₃ substrate (0°, 140°,0°);

[0105]FIG. 62 illustrates the relationship of the attenuation constant αto Θ and the thickness of tungsten electrodes when the tungstenelectrodes having various thickness values and a SiO₂ film having anormalized thickness of about 0.1 were formed on a LiTaO₃ substratehaving Euler angles (0°, Θ, 0°);

[0106]FIG. 63 illustrates the relationship of the attenuation constant αto Θ and the thickness of tungsten electrodes when the tungstenelectrodes having various thickness values and a SiO₂ film having anormalized thickness of about 0.2 were formed on a LiTaO₃ substratehaving Euler angles (0°, Θ, 0°);

[0107]FIG. 64 illustrates the relationship of the attenuation constant αto Θ and the thickness of tungsten electrodes when the tungstenelectrodes having various thickness values and a SiO₂ film having anormalized thickness of about 0.3 were formed on a LiTaO₃ substratehaving Euler angles (0°, Θ, 0°);

[0108]FIG. 65 illustrates the relationship of the attenuation constant αto Θ and the thickness of tungsten electrodes when the tungstenelectrodes having various thickness values and a SiO₂ film having anormalized thickness of about 0.4 were formed on a LiTaO₃ substratehaving Euler angles (0°, Θ, 0°);

[0109]FIG. 66 illustrates the relationship between the acoustic velocityand the normalized thickness of SiO₂ films when tungsten films havingvarious thickness values and the SiO₂ films are formed on a LiTaO₃substrate having Euler angles (0°, 126°, 0°);

[0110]FIG. 67 illustrates the relationship between the acoustic velocityand the normalized thickness of tungsten films when the tungsten filmsand SiO₂ films having various thickness values were formed on a LiTaO₃substrate having Euler angles (0°, 126°, 0°);

[0111]FIG. 68 illustrates a change in the attenuation constant α whentantalum IDTs having various thickness values and SiO₂ films havingvarious thickness values were formed on a LiTaO₃ substrate having Eulerangles (0°, 120°, 0°) according to a sixth preferred embodiment of thepresent invention;

[0112]FIG. 69 illustrates a change in the attenuation constant α whentantalum IDTs having various thickness values and SiO₂ films havingvarious thickness values were formed on a LiTaO₃ substrate having Eulerangles (0°, 140°, 0°);

[0113]FIG. 70 illustrates the relationship between the attenuationconstant α and θ when tantalum electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.1 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0114]FIG. 71 illustrates the relationship between the attenuationconstant α and Θ when tantalum electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.2 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0115]FIG. 72 illustrates the relationship between the attenuationconstant α and θ when tantalum electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.3 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0116]FIG. 73 illustrates the relationship between the attenuationconstant α and Θ when tantalum electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.4 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0117]FIG. 74 illustrates the relationship between the acoustic velocityand the normalized thickness of SiO₂ films when tantalum IDTs havingvarious thickness values and the SiO₂ films were formed on a LiTaO₃substrate having Euler angles (0°, 126°, 0°);

[0118]FIG. 75 illustrates the relationship between the acoustic velocityand the normalized thickness of tantalum IDTs when the tantalum IDTs andSiO₂ films having various thickness values were formed on a LiTaO₃substrate having Euler angles (°, 126°, 0°);

[0119]FIG. 76 illustrates a change in the attenuation constant α whenplatinum IDTs having various thickness values and SiO₂ films havingvarious thickness values were formed on a LiTaO₃ substrate having Eulerangles (0°, 125°, 0°) according to a seventh preferred embodiment of thepresent invention;

[0120]FIG. 77 illustrates a change in the attenuation constant α whenplatinum IDTs having various thickness values and SiO₂ films havingvarious thickness values are formed on a LiTaO₃ substrate having Eulerangles (0°, 140°, 0°);

[0121]FIG. 78 illustrates the relationship between the attenuationconstant α and Θ when platinum electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.1 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0122]FIG. 79 illustrates the relationship between the attenuationconstant α and Θ when platinum electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.15 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0123]FIG. 80 illustrates the relationship between the attenuationconstant α and Θ when platinum electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.2 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0124]FIG. 81 illustrates the relationship between the attenuationconstant α and Θ when platinum electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.25 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0125]FIG. 82 illustrates the relationship between the attenuationconstant α and Θ when platinum electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.3 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0126]FIG. 83 illustrates the relationship between the attenuationconstant α and Θ when platinum electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.4 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0127]FIG. 84 illustrates the relationship between the acoustic velocityand the normalized thickness of SiO₂ films when platinum IDTs havingvarious thickness values and the SiO₂ films were formed on a LiTaO₃substrate having Euler angles (0°, 126°, 0°);

[0128]FIG. 85 illustrates the relationship between the acoustic velocityand the normalized thickness of platinum IDTs when the platinum IDTs andSiO₂ films having various thickness values were formed on a LiTaO₃substrate having Euler angles (0°, 126°, 0°);

[0129]FIG. 86 illustrates a change in the attenuation constant α whennickel IDTs having various thickness values and SiO₂ films havingvarious thickness values were formed on a LiTaO₃ substrate having Eulerangles (0°, 120°, 0°) according to an eighth preferred embodiment of thepresent invention;

[0130]FIG. 87 illustrates a change in the attenuation constant α whennickel IDTs having various thickness values and SiO₂ films havingvarious thickness values were formed on a LiTaO₃ substrate having Eulerangles (0°, 140°, 0°);

[0131]FIG. 88 illustrates a change in the attenuation constant α whenmolybdenum IDTs having various thickness values and SiO₂ films havingvarious thickness values were formed on a LiTaO₃ substrate having Eulerangles (0°, 120°, 0°);

[0132]FIG. 89 illustrates a change in the attenuation constant α whenmolybdenum IDTs having various thickness values and SiO₂ films havingvarious thickness values were formed on a LiTaO₃ substrate having Eulerangles (0°, 140°, 0°);

[0133]FIG. 90 illustrates the relationship between the attenuationconstant α and θ when nickel electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.1 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0134]FIG. 91 illustrates the relationship between the attenuationconstant α and Θ when nickel electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.2 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0135]FIG. 92 illustrates the relationship between the attenuationconstant α and Θ when nickel electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.3 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0136]FIG. 93 illustrates the relationship between the attenuationconstant α and Θ when nickel electrode films having various thicknessvalues and a SiO₂ film having a normalized thickness of about 0.4 wereformed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0137]FIG. 94 illustrates the relationship between the attenuationconstant α and θ when molybdenum electrode films having variousthickness values and a SiO₂ film having a normalized thickness of about0.1 were formed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0138]FIG. 95 illustrates the relationship between the attenuationconstant α and θ when molybdenum electrode films having variousthickness values and a SiO₂ film having a normalized thickness of about0.2 were formed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0139]FIG. 96 illustrates the relationship between the attenuationconstant α and θ when molybdenum electrode films having variousthickness values and a SiO₂ film having a normalized thickness of about0.3 are formed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0140]FIG. 97 illustrates the relationship between the attenuationconstant α and Θ when molybdenum electrode films having variousthickness values and a SiO₂ film having a normalized thickness of about0.4 were formed on a LiTaO₃ substrate having Euler angles (0°, Θ, 0°);

[0141]FIG. 98 illustrates the relationship between the acoustic velocityand the normalized thickness of nickel IDTs when the nickel IDTs andSiO₂ films having various thickness values were formed on a LiTaO₃substrate having Euler angles (0°, 126°, 0°);

[0142]FIG. 99 illustrates the relationship between the acoustic velocityand the normalized thickness of SiO₂ films when nickel IDTs havingvarious thickness values and the SiO₂ films were formed on a LiTaO₃substrate having Euler angles (0°, 126°, 0°);

[0143]FIG. 100 illustrates the relationship between the acousticvelocity and the normalized thickness of molybdenum IDTs when themolybdenum IDTs and SiO₂ films having various thickness values wereformed on a LiTaO₃ substrate having Euler angles (0°, 126°, 0°);

[0144]FIG. 101 illustrates the relationship between the acousticvelocity and the normalized thickness of SiO₂ films when molybdenum IDTshaving various thickness values and the SiO₂ films were formed on aLiTaO₃ substrate having Euler angles (0°, 126°, 0°);

[0145]FIGS. 102A through 102C are schematic sectional views illustratingan etch back process for planarizing the surface of an insulating layer;

[0146]FIGS. 103A through 103D are schematic sectional views illustratinga reverse sputtering process for planarizing the surface of aninsulating layer;

[0147]FIGS. 104A and 104B are schematic sectional views illustratinganother process for planarizing the surface of an insulating layer;

[0148]FIGS. 105A through 105C are schematic sectional views illustratingstill another process for planarizing the surface of an insulatinglayer;

[0149]FIGS. 106A and 106B are schematic plan views illustrating aone-port SAW resonator and a two-port SAW resonator, respectively, towhich the present invention is applied;

[0150]FIG. 107 is a schematic plan view illustrating a ladder filter towhich the present invention is applied;

[0151]FIG. 108 is a schematic plan view illustrating a lattice filter towhich the present invention is applied;

[0152]FIGS. 109A through 109D are schematic sectional views illustratingone example of a known manufacturing method for a SAW apparatus; and

[0153]FIG. 110 illustrates a schematic sectional view illustratinganother example of a known manufacturing method for a SAW apparatus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0154] The present invention is described in detail below with referenceto the accompanying drawings through illustration of preferredembodiments of the present invention.

[0155] A manufacturing method for a SAW apparatus according to a firstpreferred embodiment of the present invention is described below withreference to FIGS. 1A through 1G, and 6.

[0156] As shown in FIG. 1A, a LiTaO₃ substrate 1 is first prepared as apiezoelectric substrate. In the first preferred embodiment of thepresent invention, a 36°-rotated Y-plate X-propagating LiTaO₃ substratehaving Euler angles (0°, 126°, 0°) is preferably used. As thepiezoelectric substrate, a LiTaO₃ substrate having different crystalorientations may be used, or a substrate made of another piezoelectricsingle crystal may be used. Alternatively, a piezoelectric substrateformed by laminating piezoelectric thin films on an insulating substratemay be used. Θ of the Euler angles (φ, Θ, ψ) can be expressed by Θ=cutangle+90°.

[0157] As shown in FIG. 1A, a first insulating layer 2 is formed on theentire surface of the LiTaO₃ substrate 1. In this preferred embodiment,the first insulating layer 2 is preferably formed of a SiO₂ film. Thefirst insulating layer 2 is formed according to a suitable techniquesuch as printing, deposition, or sputtering. The thickness of the firstinsulating layer 2 is preferably about equal to that of an IDTelectrode, which is formed in a later step.

[0158] Then, as shown in FIG. 1B, a resist pattern 3 is formed accordingto a photolithographic technique in an area other than an area in whichan IDT electrode is to be formed.

[0159] Subsequently, as indicated by the arrows in FIG. 1C, as a resultof reactive ion etching (RIE) by applying ion beams, the firstinsulating layer 2 is removed, except for the portion disposed under theresist pattern 3.

[0160] When the SiO₂ film (first insulating layer 2) is etched by RIEusing a fluorinated gas, a residue may be generated afterpolymerization. In this case, a buffered hydrofluoric acid (BHF) may beapplied after performing RIE.

[0161] Thereafter, a Cu film and a Ti film are formed such that thethickness thereof is about equal to that of the first insulating layer2. More specifically, as shown in FIG. 1D, a Cu film 4, which serves asan IDT electrode 4A, is formed on the area without the first insulatinglayer 2, and the Cu film 4 is also formed on the resist pattern 3. Then,as shown in FIG. 1E a Ti film 5 is formed as a protective metal film onthe top surface of an TDT electrode 4A and on the Cu film 4 formed onthe resist pattern 3. Accordingly, the side surfaces of the IDTelectrode 4A are covered with the first insulating layer 2, and the topsurface thereof is covered with the Ti film 5. As discussed above, theIDT electrode 4A and the protective metal film (Ti film 5) are formedsuch that the total thickness of the IDT electrode 4A and the Ti film 5are about equal to the thickness of the first insulating layer 2.

[0162] Subsequently, the resist pattern 3 is removed by using a resiststripper. Then, as shown in FIG. 1F, the IDT electrode 4A is disposed inan area other than the area in which the first insulating layer 2 isformed, and the top surface of the IDT electrode 4A is covered with theTi film 5.

[0163] Thereafter, as shown in FIG. 1G, a SiO₂ film, which serves as asecond insulating layer 6, is formed on the entire surface of the SAWapparatus.

[0164] A one-port SAW resonator 11 shown in FIG. 6 is fabricated.

[0165] In FIGS. 1A through 1G, only the portion in which the IDTelectrode 4A is formed is shown. However, as shown in FIG. 6, the SAWresonator 11 is also provided with reflectors 12 and 13 in a SAWpropagating direction such that they sandwich the IDT electrode 4Atherebetween. The reflectors 12 and 13 are also formed in the same stepsas those of the IDT electrodes 4A.

[0166] In the above-described first preferred embodiment of the presentinvention, because the one-port SAW resonator 11 is formed, only one IDTelectrode 4A is formed on the LiTaO₃ substrate 1. However, a pluralityof IDT electrodes may be formed according to the intended purpose of theSAW apparatus. Reflectors and an IDT electrode may be simultaneouslyformed. Alternatively, reflectors do not have to be formed.

[0167] For comparison, a one-port SAW resonator was formed as a firstcomparative example according to the known manufacturing method shown inFIGS. 109A through 109D for a SAW apparatus with a SiO₂ film. As in thefirst preferred embodiment of the present invention, a 36°-rotatedY-plate X-propagating LiTaO₃ substrate having Euler angles (0°, 126°,0°) was used. An IDT electrode was formed by using Cu. According to themanufacturing method shown in FIGS. 109A through 109D, because the SiO₂film 54 is formed after the IDT electrode 53A, the height of the SiO₂film 54 is not uniform. FIG. 4 shows the impedance and the phase of thefirst comparative example when the normalized thickness h/λ (hrepresents the thickness of the IDT electrode 53A and λ designates theSAW wavelength) of the IDT electrode 53A is 0.042 and when thenormalized thickness Hs/λ (Hs represents the thickness of the SiO₂ film54) of the SiO₂ film 54 is 0.11, 0.22, and 0.33. FIG. 4 shows that theratio of the impedance of the antiresonance point to the impedance ofthe resonance point, i.e., the impedance ratio, becomes smaller as thenormalized thickness Hs/λ of the SiO₂ film 54 is increased.

[0168]FIG. 5 illustrates the relationship between the normalizedthickness Hs/λ of the SiO₂ film 54 of the SAW resonator manufactured bythe known method in the first comparative example and the Figure ofMerit (MF) of the SAW resonator. FIG. 5 reveals that MF is decreased asthe normalized thickness Hs/λ of the SiO₂ film 54 becomes larger.

[0169] That is, in the first comparative example, the characteristics ofthe resonator is considerably decreased as the thickness of the SiO₂film 54 is increased, even if the IDT electrode 53A is made of Cu. Thisis probably due to the difference of the surface height of the SiO₂ film54.

[0170] The characteristics of the SAW resonator 11 manufacturedaccording to the first preferred embodiment of the present invention areshown in FIGS. 7 through 9.

[0171]FIG. 7 illustrates a change in the impedance and a change in thephase of the SAW resonator 11 manufactured according to the method ofthe above-described first preferred embodiment of the present inventionwhen the thickness of the SiO₂ film, the second insulating layer 6, ischanged. The two-dot-chain lines in FIGS. 8 and 9 indicate a change in 7and a change in MF of the SAW resonator 11, respectively, when thenormalized thickness Hs/λ of the SiO₂ film is varied. For comparison,the corresponding characteristics of the known resonator manufactured inthe first comparative example are also indicated by the solid lines inFIGS. 8 and 9.

[0172] By comparing the characteristics of FIG. 7 with those of FIG. 4,it is seen that a decrease in the impedance is small even though thenormalized thickness Hs/λ of the SiO₂ film is increased.

[0173]FIGS. 8 and 9 also show that a characteristic deterioration ofthis preferred embodiment can be suppressed even though the normalizedthickness Hs/λ of the SiO₂ film is increased.

[0174] That is, according to the manufacturing method of the firstpreferred embodiment of the present invention, a decrease in theimpedance ratio is small and a characteristic deterioration can besuppressed even though the thickness of the SiO₂ film is increased.

[0175]FIG. 10 illustrates the relationship between the temperaturecoefficient of frequency (TCF) of the SAW resonator of the firstpreferred embodiment of the present invention and that of the firstcomparative example and the thickness of the SiO₂ film. In FIG. 10, thesolid line indicates the first comparative example, and thetwo-dot-chain line indicates the first preferred embodiment of thepresent invention.

[0176]FIG. 10 indicates that the TCF can be ideally improved byincreasing the thickness of the SiO₂ film according to the manufacturingmethod of the first preferred embodiment of the present invention.

[0177] Thus, according to the manufacturing method of the firstpreferred embodiment of the present invention, it is possible to providea SAW resonator in which the characteristic deterioration can besuppressed and the TCF can be effectively improved.

[0178] Additionally, according to the manufacturing method of the firstpreferred embodiment of the present invention, because the IDT electrode4A is made of Cu, which has a density higher than Al, it has asufficient reflection coefficient, thereby suppressing the generation ofundesirable ripples in the resonance characteristic. This is describedin detail below.

[0179] For comparison, a SAW resonator was formed as a secondcomparative example in a manner similar to the first preferredembodiment of the present invention, except that Al was used for the IDTelectrode instead of Cu and the normalized thickness Hs/λ of the SiO₂film, the first insulating layer, was about 0.08. The impedance and thephase of the SAW resonator of the second comparative example areindicated by the solid lines of FIG. 11.

[0180] The impedance and the phase of the SAW resonator formed in amanner similar to the second comparative example, except that a SiO₂film was not formed, are indicated by the broken lines in FIG. 11.

[0181] The solid lines of FIG. 11 indicate that large ripples (indicatedby the arrows A) are generated between the resonance point and theantiresonance point when the IDT electrode was formed of Al and the SiO₂film was formed in the second comparative example. In contrast, thebroken lines of FIG. 11 indicate that such ripples are not generated inthe SAW resonator without the SiO₂ film.

[0182] Accordingly, even though the SiO₂ film was formed to improve theTCF, the above-described ripples A are generated if the IDT electrode isformed by using Al, resulting in a characteristic deterioration. Afterfurther studying this point, the present inventors discovered that thereflection coefficient of the IDT electrode can be increased by using ametal having a density higher than Al for the IDT electrode so as tosuppress the above-described ripples A.

[0183] Then, a SAW resonator was formed in a manner similar to theabove-described first preferred embodiment of the present invention,except that the density of the metal for the IDT electrode was varied.The impedances of the SAW resonators using metals with differentdensities are shown in FIGS. 12A through 12E. FIGS. 12A through 12Eillustrate the impedances when the ratio

1/

2 of the average density

1 of the laminated structure including the IDT electrode and theprotective metal film to the density

2 of the first insulating layer is about 2.5, 2.0, 1.5, 1.2, and 1.0,respectively.

[0184]FIGS. 12A through 12C show that the ripples A are shifted to therange outside the pass band, and more particularly, FIG. 12A shows thatthe ripples A are considerably suppressed.

[0185] Accordingly, as is seen from FIGS. 12A through 12E, the ripples Acan be shifted to the range outside the band pass between the resonantfrequency and the antiresonant frequency when the density ratio of thelaminated structure including the IDT electrode and the protective metalfilm to the first insulating layer is about 1.5 or greater, therebyhaving improved characteristics. When the density ratio is about 2.5 orgreater, the ripples can be considerably suppressed.

[0186] In the examples of FIGS. 12A through 12E, because the Ti film islaminated on the IDT electrode 4A, the average density was calculated.However, in the preferred embodiments of the present invention, theprovision of the protective metal film on an IDT is not essential. Inthis case, the thickness of the IDT electrode is preferably about equalto that of the first insulating layer, and the ratio of the density ofthe IDT electrode to that of the first insulating layer is preferablyabout 1.5 or greater, and more preferably, about 2.5 or greater. Then,advantages similar to those obtained by the above-described example canbe achieved.

[0187] Accordingly, in a SAW resonator in which a SiO₂ film is formed tocover an IDT electrode, the reflection coefficient of the IDT electrodecan be increased if the density of the IDT electrode, or the averagedensity of a laminated structure including the IDT electrode and aprotective metal film, is preferably greater than the density of a firstinsulating layer disposed along the side surfaces of the IDT electrode,thereby suppressing the generation of ripples between the resonancepoint and the antiresonance point.

[0188] A metal or an alloy having a higher density than Al includes, notonly Cu, but also Ag or Au or an alloy essentially consisting of Ag orAu.

[0189] As in the first preferred embodiment of the invention, aprotective metal film is preferably disposed on the IDT electrode. Then,according to the manufacturing method shown in FIGS. 1A through 1G, whenthe resist pattern 3 is removed, the erosion of the IDT electrode 4A canbe prevented because the side surfaces of the IDT electrode 4A arecovered with the first insulating layer 2 and the top surface thereof iscovered with the protective metal film 5. It is thus possible to providea SAW resonator having superior characteristics.

[0190] The first and second insulating layers may be formed by aninsulating material other than SiO₂, such as SiO_(x)N_(y), whichcontributes to an improvement in the temperature characteristics. Thefirst and second insulating layers may be made of the same insulatingmaterials, as the first preferred embodiment of the present invention,or they may be formed of different insulating materials.

[0191]FIG. 13 illustrates the relationship between the electromechanicalcoupling coefficient and the normalized thickness H/λ of IDT electrodesmade of various metals and having various thickness values on a LiTaO₃substrate having Euler angles (0°, 126°, 0°).

[0192] The types of metals having larger electromechanical coefficientsthan Al were extracted from FIG. 13, and the normalized thickness valuesof such metals are shown in FIG. 14. That is, FIG. 14 illustrates theelectrode thickness range that exhibits greater electromechanicalcoefficients than Al.

[0193] In FIG. 14, the upper limit of the thickness range of the IDTelectrodes indicates the threshold for having a greaterelectromechanical coupling coefficient than Al, and the lower limit ofthe thickness range represents the thickness of the IDT electrode thatcan be manufactured. By approximating the upper limit to a quadraticexpression when the electrode thickness range having greaterelectromechanical coupling coefficients is y and the density is x, theequation y=0.00025x²−0.01056x+0.16473 can be found.

[0194] Accordingly, as is seen from subsequent preferred embodiments inwhich SAW resonators are formed by specifying electrode materials, it isnow assumed that an IDT electrode is formed on a 14°-50°-rotated Y-plateX-propagating LiTaO₃ piezoelectric substrate having Euler angles (0°,104°-140°, 0°), and the normalized thickness Hs/λ of a SiO₂ film rangesfrom about 0.03 to about 0.45. In this case, the electromechanicalcoupling coefficient can be increased, as shown in FIG. 14, when thenormalized thickness H/λ of the IDT electrode satisfies the followingexpression (1):

0.005≦H/λ0.00025×

²−0.01056×

+0.16473  (1)

[0195] wherein

represents the average density of the IDT electrode.

[0196] In preferred embodiments of the present invention, a metal havinga higher density than Al is preferably used for the IDT electrode. Inthis case, the IDT electrode may be made of a metal having a higherdensity than Al or an alloy primarily including a metal having a higherdensity than Al Alternatively, the IDT electrode may be formed of alaminated structure including a primary metallic film made of a metalhaving a higher density than Al or an alloy primarily including a metalhaving a higher density than Al and a secondary metallic film made of ametal different from that of the primary metallic film. In this case,the average density of the laminated film preferably satisfies theexpression represented by

0×0.7≦

≦

0×1.3 where

indicates the average density of the IDT electrode and

0 designates the density of the primary metallic film.

[0197] In preferred embodiments of the present invention, as describedabove, the surface of the second insulating layer is planarized.However, the height of the second insulating film may be differentwithin a range of about 30% or smaller of the thickness of the IDTelectrode. If this height difference exceeds about 30%, the advantageachieved by the planarized level of the second insulating layer cannotbe sufficiently obtained.

[0198] The second insulating layer can be planarized by varioustechniques, such as by performing an etch back process, by utilizing anoblique incidence effect by means of reverse sputtering, by polishingthe surface of the insulating layer, and by polishing the electrode. Theplanarization of the second insulating layer may be performed by acombination of two or more types of the above-described techniques.Details of such techniques are discussed below with reference to FIGS.102A through 105C.

[0199]FIGS. 102A through 102C are schematic sectional views illustratinga planarization technique for the surface of the insulating layeraccording to an etch back process. As shown in FIG. 102A, an electrode42 is first formed on a piezoelectric substrate 41, and then, aninsulating layer 43 is formed of, for example, SiO₂. As shown in FIG.102B, a resist pattern 44 is formed on the insulating layer 43 by, forexample, spin coating. In this case, the surface of the resist pattern44 is flat. Thus, by etching the resist pattern 44 according to RIE,i.e., by an etch back process, the surface of the insulating layer 43can be planarized, as shown in FIG. 102C.

[0200]FIGS. 103A through 103D are schematic sectional views illustratingthe reverse sputtering process. The electrode 42 is first formed on thepiezoelectric substrate 41, and then, the insulating layer 43 is formed.Then, argon ions, which are used for sputtering the substrate 41, areapplied onto the surface of the insulating layer 43 by sputtering. Whensputtering is performed by ion bombardment on the surface of thesubstrate, a greater sputtering effect is produced if ions are appliedonto an oblique surface rather than a flat surface. This is known as the“oblique incidence effect”. Due to this effect, the insulating layer 43is planarized as the sputtering proceeds, as shown in FIGS. 103B through103D.

[0201]FIGS. 104A and 104B are schematic sectional views illustrating aplanarization technique by polishing the insulating layer. As shown inFIG. 104A, after the electrode 42 and the insulating layer 43 are formedon the substrate 41, the insulating layer 43 is mechanically orchemically polished so as to be planarized.

[0202]FIGS. 105A through 105C are schematic sectional views illustratinga planarization technique by polishing the electrode. As shown in FIG.105A, a first insulating layer 45 is formed on the substrate 41, and ametallic film 42A, which is made of an electrode material, is formed onthe entire surface by deposition. Then, as shown in FIG. 105B, bymechanically or chemically polishing the metallic film 42A, theelectrode 42 and the first insulating layer 45, which is disposed aroundthe electrode 42, are formed. Thus, the first insulating layer 45 andthe electrode 42 are planarized so that they are flush with each other.Thereafter, as shown in FIG. 105C, a second insulating layer 46 isformed. According to this technique, the surface of the insulating layeris planarized.

[0203] The present invention is applicable to various types of SAWapparatuses. Examples of such SAW apparatuses are shown in FIGS. 106Athrough 108. FIGS. 106A and 106B are schematic plan views illustrating aone-port SAW resonator 47 and a two-port SAW resonator 48, respectively.By using the same electrode structure as that of the two-port SAWresonator 48 shown in FIG. 106B, a two-port SAW resonator filter may beformed.

[0204]FIGS. 107 and 108 are schematic plan views illustrating theelectrode structures of a ladder filter 49 a and a lattice filter 49 b,respectively. By forming the electrode structure of the ladder filter 49a and the lattice filter 49 b on the piezoelectric substrate, a ladderfilter and a lattice filter can be formed according to the presentinvention.

[0205] The present invention is not restricted to the SAW apparatuseshaving the electrode structures shown in FIGS. 106A, 106B, and 107, andmay be used in various types of SAW apparatuses.

[0206] In preferred embodiments of the present invention, preferably, aSAW apparatus using a leaky SAW is manufactured. Japanese UnexaminedPatent Application Publication No. 6-164306 discloses a SAW apparatushaving an electrode made of a heavy metal, such as Au, and utilizing theLove wave, which is free from the propagation attenuation. In this SAWapparatus, by using a heavy metal for the electrode, the acousticvelocity of a propagating SAW becomes lower than that of a transversalbulk wave in the substrate so as to eliminate leaky components. In thismanner, the Love wave is utilized as a non-leaky SAW.

[0207] In the Love wave, however, because the acoustic velocityinevitably becomes low, and accordingly, the IDT pitch must bedecreased. This increases the difficulty in processing the SAWapparatus, thereby decreasing the processing precision. Additionally,the linewidth of the IDT becomes smaller, and the loss caused by theresistance is increased.

[0208] In preferred embodiments of the present invention, unlike theabove-described SAW apparatus utilizing the Love wave, even though theelectrode made of a metal heavier than Al is used, a leaky SAW having ahigh acoustic velocity can be effectively utilized, thereby achieving areduction in the propagation loss. It is thus possible to provide alow-insertion SAW apparatus.

[0209] Based on the above-described results, electrodes were formed byusing different metals having a higher density than Al.

[0210] Metals having a higher density than Al used in preferredembodiments the present invention include, for example:

[0211] (1) a metal having a density of 15000 to 23000 kg/m³ and aYoung's modulus of 0.5×10¹¹ to 1.0×10¹¹ N/m² or having atransversal-wave acoustic velocity of 1000 to 2000 m/s, for example, Au;

[0212] (2) a metal having a density of 5000 to 15000 kg/m³ and a Young'smodulus of 0.5×10¹¹ to 1.0×10¹¹ N/m² or having a transversal-waveacoustic velocity of 1000 to 2000 m/s, for example, Ag;

[0213] (3) a metal having a density of 5000 to 15000 kg/m³ and a Young'smodulus of 1.0×10¹¹ to 2.05×10¹¹N/m² or having a transversal-waveacoustic velocity of 2000 to 2800 m/s, for example, Cu;

[0214] (4) a metal having a density of 15000 to 23000 kg/m³ and aYoung's modulus of 2.0×10¹¹ to 4.5×10¹¹ N/m² or having atransversal-wave acoustic velocity of 2800 to 3500 m/s, for example,tungsten;

[0215] (5) a metal having a density of 15000 to 23000 kg/m³ and aYoung's modulus of 1.0×10¹¹ to 2.0×10¹¹N/m² or having a transversal-waveacoustic velocity of 2000 to 2800 m/s, for example, tantalum;

[0216] (6) a metal having a density of 15000 to 23000 kg/m³ and aYoung's modulus of 1.0×10¹¹ to 2.0×10¹¹ N/m² or having atransversal-wave acoustic velocity of 1000 to 2000 m/s, for example,platinum; and

[0217] (7) a metal having a density of 5000 to 15000 kg/m³ and a Young'smodulus of 2.0×10¹¹ to 4.5×10¹¹ N/m² or having a transversal-waveacoustic velocity of 2800 to 3500 m/s, for example, Ni and Mo.

[0218]FIG. 15 is a plan view illustrating a longitudinally coupledresonator filter as a SAW apparatus 21 according to a second preferredembodiment of the present invention. In the second preferred embodimentof the present invention, Au is preferably used for electrodes.

[0219] In the SAW apparatus 21, IDTs 23 a and 23 b and reflectors 24 aand 24 b are formed on the top surface of a LiTaO₃ substrate 22. A SiO₂film 25 is formed to cover the IDTs 23 a and 23 b and the reflectors 24a and 24 b. As the LiTaO₃ substrate 22, a 25°-58°rotated Y-plateX-propagating LiTaO₃ substrate having Euler angles (0°, 115°-148°, 0°)is preferably used. If a Y-plate X-propagating LiTaO₃ substrate having acut angle other than the above range is used, the attenuation constantis increased, and the TCF is deteriorated.

[0220] The IDTs 23 a and 23 b and the reflectors 24 a and 24 b are madeof a metal having a density higher than Al. At least one metal selectedfrom the group including Au, Pt, W, Ta, Ag, Mo, Cu, Ni, Co, Cr, Fe, Mn,Zn, and Ti, or an alloy primarily including at least one metal of theabove-described group may be used as the metal having a density higherthan Al.

[0221] As described above, because the IDTs 23 a and 23 b and thereflectors 24 a and 24 b are made of a metal having a density higherthan Al, the electromechanical coupling coefficient and the reflectioncoefficient are improved, as shown in FIGS. 16 and 17, respectively,even when the thickness of the IDTs 23 a and 23 b and that of thereflectors 24 a and 24 b are formed to be smaller compared to the IDTsand the reflectors made of Al.

[0222] The thickness of the electrodes can be decreased, as statedabove. The thickness of the SiO₂ film 25 is preferably determined sothat the thickness Hs/λ standardized by the SAW wavelength λ ranges fromabout 0.03 to about 0.45, which can be clearly seen in the subsequentexamples. In this case, Hs indicates the total thickness of the firstand the second SiO₂ insulating layers. With this range, the attenuationconstant can be considerably decreased compared to a SAW apparatuswithout a SiO₂ film, thereby achieving a reduction in the loss.

[0223] The ideal thickness of the IDTs 23 a and 23 b standardized by theSAW wavelength is different according to the material forming the IDTs23 a and 23 b. If the IDTs are made of Au, the normalized thickness ofthe IDTs 23 a and 23 b is preferably from about 0.013 to about 0.030. Ifthe Au film is too thin, the IDTs 23 a and 23 b exhibit a resistance.Accordingly, the normalized thickness of the IDTs 23 a and 23 b is, morepreferably, from about 0.021 to about 0.030.

[0224] According to the SAW apparatus of the second preferred embodimentof the present invention, the IDTs 23 a and 23 b are made of a metalhaving a density higher than Al on the LiTaO₃ substrate 22, and thethickness of the IDTs 23 a and 23 b can be decreased. Thus, the SAWapparatus exhibits improved characteristics and also improves the TCF bythe formation of the SiO₂ film 25. This is described in greater detailby specific examples.

[0225] The electromechanical coupling coefficient K_(SAW), thereflection coefficient |ref|, and the attenuation constant (a) withrespect to the normalized thickness of IDTs when the IDTs were made ofAl, Au, Ta, Ag, Cr, W, Cu, Zn, Mo, and Ni on a 36°-rotated Y-plateX-propagating LiTaO₃ substrate having Euler angles (0°, 126°, 0°) areshown in FIGS. 16, 17, and 18, respectively. It should be noted thatcalculations were made according to the method indicated in J. J.Chambell and W. R. Jones: IEEE Trans. Sonic & Ultrason. SU-15. p209(1968), assuming that the electrodes were uniformly formed.

[0226]FIG. 16 shows that, in the IDT made of Al, the electromechanicalcoupling coefficient K_(SAW) is about 0.27 when the normalized thicknessH/I (H represents the thickness of the IDT and λ designates thewavelength) is about 0.10. In contrast, in the IDTs made of Au, Ta, Ag,Cr, W, Cu, Zn, Mo, and Ni, higher electromechanical couplingcoefficients K_(SAW) are achieved when H/λ ranges from about 0.013 toabout 0.035. FIG. 18 reveals that, however, in the IDTs made of Au, Ta,Ag, Cr, W, Cu, Zn, Mo, and Ni, the attenuation constants α become verylarge, while, in the IDT made of Al, the attenuation constant α issubstantially 0 regardless of the normalized thickness H/λ.

[0227]FIG. 25 illustrates the relationship between the electromechanicalcoupling coefficient and Θ of the Euler angles (0°, Θ, 0°) when the AuIDT and the SiO₂ film are formed on a LiTaO₃ substrate having Eulerangles (0°, Θ, 0°). In this case, the normalized thickness of the IDTwas changed to about 0.022, 0.025, and 0.030, and the normalizedthickness Hs/λ of the SiO₂ film was changed to about 0.00 (without SiO₂film), 0.10, 0.20, 0.30, and 0.45.

[0228]FIG. 25 shows that the electromechanical coupling coefficientK_(SAW) becomes smaller as the thickness of the SiO₂ film is increased.It is now assumed that the thickness of the IDT is decreased forsuppressing a characteristic deterioration caused by the formation ofSiO₂ film, which is described in detail below. FIG. 16 shows that theelectromechanical coupling coefficient K_(SAW) is decreased to about0.245 when the normalized thickness of the Al IDT is reduced to about0.04 without the formation of SiO₂ film. If the normalized thickness ofthe Al IDT is reduced to about 0.04 with the formation of a SiO₂ film,the electromechanical coupling coefficient K_(SAW) becomes even smaller,which makes it difficult to achieve a wider band when the resulting SAWapparatus is put to practical use.

[0229] In contrast, as is seen from FIG. 25, when the IDT is formed ofAu and a SiO₂ film is formed, the electromechanical coupling coefficientK_(SAW) can be increased to about 0.245 or greater by setting Θ of theEuler angles to be about 128.5° or smaller even though the normalizedthickness Hs/λ of the SiO₂ film is about 0.45. When the normalizedthickness of the SiO₂ film is about 0.30, the electromechanical couplingcoefficient K_(SAW) can be increased to about 0.245 or greater bysetting Θ of the Euler angles to be about 132° or smaller. As discussedbelow, when Θ of the Euler angles is smaller than 115°, the attenuationconstant is increased, which makes it difficult put the SAW apparatus topractical use. Thus, preferably, a 25°-42°-rotated Y-plate X-propagatingLiTaO₃ substrate having Euler angles (0±3°, 115°-132°, 0±3°), and morepreferably, a 25°-38.5°-rotated Y-plate X-propagating LiTaO₃ substratehaving Euler angles (0±3°, 115°-128.5°, 0±3°) is used.

[0230] The temperature coefficient of frequency (TCF) of a 36°-rotatedY-plate X-propagating LiTaO₃ substrate having Euler angles (0°, 126°,0°) is −30 to −40 ppm/° C., which is not sufficient. In order to improvethe TCF to be about ±20 ppm/° C., an Au IDT was formed on a 36°-rotatedY-plate X-propagating LiTaO₃ substrate having Euler angles (0°, 126°,0°), and the thickness of the SiO₂ film was changed. In this case, theTCF with respect to the normalized thickness of the SiO₂ film is shownin FIG. 19. In FIG. 19, ◯ indicates the ideal values, and x designatesthe values measured. In this case, the normalized thickness H/λ of theAu IDT is about 0.020.

[0231]FIG. 19 shows that the formation of the SiO₂ film improves theTCF, and in particular, when the normalized thickness Hs/λ of the SiO₂film is about 0.25, the TCF becomes substantially zero.

[0232] Also, by using two types of rotated Y-plate X-propagating LiTaO₃substrates, i.e., a substrate having a cut angle of 36° (Euler angles(0°, 126°, 0°)), and a substrate having a cut angle of 38° (Euler angles(0°, 128°, 0°)), the normalized thickness H/λ of an Au IDT and thenormalized thickness Hs/λ of a SiO₂ film were changed. The attenuationconstants α with respect to the normalized thickness of the SiO₂ filmare shown in FIGS. 20 and 21. FIGS. 20 and 21 show that the attenuationconstant α can be made smaller if the thickness of the SiO₂ film issuitably selected regardless of the thickness of the IDT. Morespecifically, as is seen from FIGS. 20 and 21, if the normalizedthickness Hs/λ of the SiO₂ film ranges from about 0.03 to about 0.45,and more preferably, from about 0.10 to about 0.35, the attenuationconstant α can be reduced to a minimal level regardless of theabove-described two types of Euler angles of the LiTaO₃ substrate andthe thickness of the Au IDT.

[0233]FIG. 17 shows that the use of an Au IDT achieves a sufficientlylarge reflection coefficient even with a small thickness of the IDTcompared to an Al IDT.

[0234] Thus, according to the results of FIGS. 16 through 21, when an AuIDT having a normalized thickness H/λ of about 0.013 to about 0.030 isformed on a LiTaO₃ substrate, a large electromechanical couplingcoefficient can be achieved, and also, the attenuation coefficient α canbe reduced to a minimal level, and a sufficient reflection coefficientcan be implemented if the normalized thickness Hs/λ of the SiO₂ film ispreferably within the range from about 0.03 to about 0.45.

[0235] In the second preferred embodiment of the present invention, theSAW apparatus 11 was manufactured by forming an Au TDT having anormalized thickness H/λ of about 0.020 and a SiO₂ film having anormalized thickness Hs/λ of about 0.1 on a LiTaO₃ substrate having acut angle of 36° (Euler angles (0°, 126°, 0°)). Theattenuation-vs.-frequency characteristic of the SAW apparatus 11 isindicated by the broken line of FIG. 22. For comparison, theattenuation-vs.-frequency characteristic of the SAW apparatus 11 beforethe formation of the SiO₂ film is also indicated by the solid line ofFIG. 22.

[0236]FIG. 22 shows that, because of the formation of the SiO₂ film, theinsertion loss is decreased even though the electromechanical couplingcoefficient is slightly reduced from about 0.30 to about 0.28.Accordingly, it has been proved that the attenuation constant α can bedecreased if the thickness of the SiO₂ film is set to theabove-described specific range.

[0237] After discovering the above-described fact, the present inventorsformed one-port SAW resonators on an experimental basis by forming an AuIDT having a normalized thickness of about 0.02 and a SiO₂ film onrotated Y-plate X-propagating LiTaO₃ substrates having different Eulerangles. In this case, the normalized thickness of the SiO₂ film waschanged to about 0.10, 0.20, 0.30, and 0.45. The Q factors of theone-port SAW resonators are shown in FIG. 26.

[0238] Generally, as the Q factor of a resonator is increased, thesharpness of the filter characteristic of the resonator from the passband to the attenuation range is increased. Accordingly, if a sharpfilter characteristic is required, a greater Q factor is desirable. Asis seen from FIG. 26, when the cut angle of the substrate is about 48°(Euler angles of about (0°, 138°, 0°)), the Q factor becomes maximum,and when the cut angle ranges from about 42° to about 58° (Euler anglesof about of (0°, 132°-148°, 0°)), the Q factor becomes comparativelylarge regardless of the thickness of the SiO₂ film.

[0239] Accordingly, as is seen from FIG. 26, by forming a SAW resonatorsuch that at least one IDT made of a metal having a density higher thanAl is formed on a Y-plate LiTaO₃ substrate having a cut angle of about42° to about 58° (Euler angles of about (0°, 132°-148°, 0°)), and a SiO₂film is formed to cover the IDT on the LiTaO₃ substrate, a large Qfactor can be obtained. It is preferable that the cut angle of theLiTaO₃ substrate is about 46.5° to about 53° (Euler angles of about (0°,136.5°-143°, 0°)), as can be seen from FIG. 26.

[0240] In preferred embodiments the present invention, a contact layermay be formed on the top surface of the IDT. More specifically, as shownin FIG. 27A, an IDT 33 is formed on a LiTaO₃ substrate 32, and a contactlayer 34 may be formed on the top surface of the IDT 33. The contactlayer 34 is disposed between the IDT 33 and a SiO₂ film 35, so that itincreases the contact strength of the SiO₂ film 35 to the IDT 33. As thematerial for the contact layer 34, Pd or Al, or an alloy thereof may besuitably used. The contact layer 34 is not restricted to a metal, and apiezoelectric material, such as ZnO, or ceramics, such as Ta₂O₃ orAl₂O₃, may be used. The formation of the contact layer 34 increases thecontact strength between the IDT 33 and the SiO₂ film 35, therebypreventing the SiO₂ film 35 from peeling off.

[0241] The thickness of the contact layer 34 is preferably about 1% orless of the SAW wavelength so as to minimize the influence on the SAW bythe formation of the contact layer 34. Although the contact layer 34 isformed only on the top surface of the IDT 33 in FIG. 27A, it may also beformed at the interface between the LiTaO₃ substrate 33 and the SiO₂film 35, as shown in FIG. 27B. Alternatively, as shown in FIG. 27C, thecontact layer 34 may also be formed, not only on the top surface of theIDT 33, but also on the side surfaces of the IDT 33.

[0242] As another configuration for improving the contact strength ofthe SiO₂ film, a plurality of electrodes including bus bars andexternally connecting pads other than IDTs may be laminated with anunderlying metal layer formed of the same material as the IDT, and anupper metal layer made of Al or an Al alloy laminated with theunderlying metal layer. For example, as an electrode film forming thereflectors 24 a and 24 b shown in FIG. 15, an underlying metal layermade of the same material as the IDTs 23 a and 23 b and an Al film maybe laminated on the underlying metal layer. Accordingly, by providing anupper metal layer made of Al or an Al alloy, the contact strength of theSiO₂ film can be enhanced. Additionally, the cost of the electrode canbe reduced, and the Al wedge bonding can also be enhanced.

[0243] The electrodes other than IDTs include, not only reflectors, busbars, and externally connecting pads, but also wiring electrodes, whichare formed if necessary. The Al alloy may include an Al-Ti alloy or anAl-Ni-Cr alloy by way of examples only.

[0244] The present inventors have confirmed that there is a certainrange of thickness of the SiO₂ film that minimizes the attenuationconstant α as long as an Au IDT is formed even when a Y-plateX-propagating LiTaO₃ substrate having Euler angles other than theabove-described angles is used. That is, if the normalized thicknessHs/λ of the SiO₂ film is set to be a specific range, the attenuationconstant α can be reduced, as in the above-described example. Therelationship between the attenuation constant α and the Euler angle Θwhen the normalized thickness Hs/λ of the SiO₂ film was about 0.1 toabout 0.45 are shown in FIGS. 28 through 35. FIGS. 28 through 35 showthat the Euler angle Θ that minimizes the attenuation constant α becomessmaller as the thickness of the SiO₂ film is increased. Accordingly,even when a Y-plate X-propagating LiTaO₃ substrate having Euler anglesother than the above-described angles is used, it is possible to providea SAW apparatus that exhibits a large electromechanical couplingcoefficient and a large reflection coefficient and that reduces the TCFto one half of the known SAW apparatus if an Au IDT and a SiO₂ film areused. Preferable combinations of the Euler angles, the thickness of theAu IDT, and the thickness of the SiO₂ film that achieve theabove-described advantages are shown in Table 1 and Table 2. TABLE 1SiO₂ film Θ of Euler angles Au thickness thickness (0 ± 3°, Θ, 0 ± 3°)H/λ Hs/λ 120.0° ≦ Θ < 123.0° 0.013-0.018 0.15-0.45 123.0° ≦ Θ < 124.5°0.013-0.022 0.10-0.40 124.5° ≦ Θ < 125.5° 0.013-0.025 0.07-0.40 125.5° ≦Θ < 127.5° 0.013-0.025 0.06-0.40 127.5° ≦ Θ < 129.0° 0.013-0.0280.04-0.40 129.0° ≦ Θ < 130.0° 0.017-0.030 0.03-0.42 130.0° ≦ Θ < 131.5°0.017-0.030 0.03-0.42 131.5° ≦ Θ < 133.0° 0.018-0.028 0.05-0.33 133.0° ≦Θ < 135.0° 0.018-0.030 0.05-0.30 135.0° ≦ Θ < 137.0° 0.019-0.0320.05-0.25 137.0° ≦ Θ ≦ 140.0° 0.019-0.032 0.05-0.25

[0245] TABLE 2 SiO₂ film Θ of Euler angles Au thickness thickness (0 ±3°, Θ, 0 ± 3°) H/λ Hs/λ 129.0° ≦ Θ < 130.0° 0.022-0.028 0.04-0.40 130.0°≦ Θ < 131.5° 0.022-0.028 0.04-0.40 131.5° ≦ Θ < 133.0° 0.022-0.0280.05-0.33 133.0° ≦ Θ < 135.0° 0.022-0.030 0.05-0.30 135.0° ≦ Θ < 137.0°0.022-0.032 0.05-0.25 137.0° ≦ Θ ≦ 140.0° 0.022-0.032 0.05-0.25

[0246] Euler angle Θ may sometimes deviate from the desired angle by −2°to +4°. This deviation is caused by the fact that calculations were madein this preferred embodiment assuming that a metallic film was formed onthe entire surface of the substrate, and there may be some errors withinthe above range in actual SAW apparatuses.

[0247] When manufacturing the SAW apparatus according to the preferredembodiments of the present invention, it is preferable that an IDTprimarily including Au is formed on a rotated Y-plate X-propagatingLiTaO₃ substrate. In this state, the frequency of the SAW apparatus isadjusted. Then, a SiO₂ film, having a thickness reduces the attenuationconstant α, is formed. This is explained below with reference to FIGS.23 and 24. Au IDTs having different thickness values and SiO₂ filmshaving different thickness values were formed on a 36°-rotated Y-plateX-propagating LiTaO₃ substrate (Euler angles (0°, 126°, 0°)). FIG. 23illustrates a change in the acoustic velocity of a leaky SAW withrespect to the thickness of the IDT. FIG. 24 illustrates a change in theacoustic velocity of a leaky SAW with respect to the thickness of theSiO₂ film. FIGS. 23 and 24 show that a change in the acoustic velocityof the SAW is much larger when the thickness of the IDT is varied thanwhen the thickness of the SiO₂ film is varied. Accordingly, it isdesirable that the frequency is adjusted before the formation of theSiO₂ film. For example, it is desirable that the frequency is adjustedafter an Au IDT is formed by laser etching or ion etching. Morepreferably, the normalized thickness of the Au IDT ranges from about0.015 to about 0.030. In this case, a change in the acoustic velocity bya variation of a SiO₂ film is reduced, and a frequency fluctuation dueto a variation of the SiO₂ film is decreased.

[0248] Θ of the Euler angles may sometimes deviate from the desiredangle by about −2° to about +4°. This deviation is caused by the factthat calculations were made in this preferred embodiment assuming that ametallic film was formed on the entire surface of the substrate, andthere may be some errors within the above range in actual SAWapparatuses.

[0249] When manufacturing SAW apparatuses, although φ and ψ of the Eulerangles deviate from 0° by ±3°, substantially the same characteristic asthat when φ and ψ are 0° can be obtained.

[0250] A SAW apparatus of a third preferred embodiment of the presentinvention is described below. The SAW apparatus of the third preferredembodiment of the present invention is similar to the SAW apparatus 21of the second preferred embodiment of the present invention shown inFIG. 15, except that the IDTs 23 a and 23 b are preferably made of Ag.

[0251] As stated below, when the IDTs 23 a and 23 b are made of Ag, thethickness H/λ of the IDTs 23 a and 23 b standardized by the SAWwavelength λ is preferably from about 0.01 to about 0.08.

[0252] According to the SAW apparatus of the third preferred embodimentof the present invention, the IDTs 23 a and 23 b are made of Ag on theLiTaO₃ substrate 22 and the thickness of the IDTs 23 a and 23 b can bedecreased. Because the LiTaQ₃ substrate is used, the attenuationconstant can be considerably decreased, thereby achieving low insertionloss. By the formation of the SiO₂ film 25, a high level of temperaturecoefficient of frequency (TCP) is achieved. This is described in detailbelow by way of specific examples.

[0253] SAWs propagating in a LiTaO₃ substrate include, not only Rayleighwave, but also leaky SAW (LSAW). Although the LSAW has a higher acousticvelocity and a greater electromechanical coupling coefficient than theRayleigh wave, it propagates while radiating energy in the substrate.Accordingly, the LSAW causes attenuation which results in the insertionloss.

[0254]FIG. 36 illustrates the relationship between the electromechanicalcoupling coefficient K_(SAW) and the normalized thickness H/λ of an AgIDT on a 36°-rotated Y-plate X-propagating LiTaO₃ substrate (havingEuler angles (0°, 126°, 0°)). It should be noted that λ represents thewavelength at the center frequency of the SAW apparatus.

[0255]FIG. 36 shows that, when the thickness H/λ of the Ag film rangesfrom about 0.01 to about 0.08, the electromechanical couplingcoefficient K_(SAW) becomes about 1.5 times or greater than theelectromechanical coupling coefficient of a SAW apparatus without an Agfilm (H/λ=0). When the thickness H/λ of the Ag film ranges from about0.02 to about 0.06, the electromechanical coupling coefficient K_(SAW)becomes about 1.7 times or greater than the electromechanical couplingcoefficient of a SAW apparatus without an Ag film. When the thicknessH/λ of the Ag film ranges from about 0.03 to about 0.05, theelectromechanical coupling coefficient K_(SAW) becomes about 1.8 timesor greater than the electromechanical coupling coefficient of a SAWapparatus without an Ag film.

[0256] If the thickness H/λ of the Ag film exceeds about 0.08, itbecomes difficult to form an Ag IDT. Accordingly, in order to obtain alarge electromechanical coupling coefficient without a difficulty informing an Ag IDT, the thickness of the Ag IDT is desirably from about0.01 to about 0.08, and more preferably, from about 0.02 to about 0.06,and further preferably, about 0.03 to about 0.05.

[0257] The relationship between the TCF and the thickness Hs/λ of a SiO₂film formed on a LiTaO₃ substrate is shown in FIG. 37. FIG. 37 shows theresults obtained when three types of LiTaO₃ substrates having Eulerangles (0°, 113°, 0°), (0°, 126°, 0°), (0°, 129°, 0°) were used. In thisexample, an electrode is not formed.

[0258]FIG. 37 reveals that the TCF ranges from about −20 to about +20ppm/° C. when the thickness Hs/λ of the SiO₂ film is from about 0.15 toabout 0.45, regardless of whether the angle Θ is 113°, 126°, or 129°.Because of the time it takes to form a SiO₂ film, the thickness Hs/λ ofthe SiO₂ film is desirably about 0.15 to about 0.40.

[0259]FIG. 38 illustrates a change in the attenuation constant α when Agelectrodes having a normalized thickness H/λ of about 0.10 or smallerand SiO₂ films having a normalized thickness Hs/λ of 0 to about 0.5 wereformed on a LiTaO₃ substrate having Euler angles (0°, 120°, 0°). FIG. 38shows that the attenuation constant α is small when the thickness Hs/λof the SiO₂ film is about 0.2 to about 0.4, and when the thickness H/λof the Ag film is about 0.01 to about 0.10.

[0260]FIG. 39 illustrates a change in the attenuation constant α when Agelectrodes having a normalized thickness H/λ of 0 to about 0.10 and SiO₂films having a normalized thickness Hs/λ of 0 to about 0.5 were formedon a LiTaO₃ substrate having Euler angles (0°, 140°, 0°). As is seenfrom FIG. 39, when Θ is 140°, the attenuation constant α becomes largeras the thickness of the SiO₂ film is increases, as described above, andas the normalized thickness of the Ag film decreases, especially whenthe normalized thickness of the Ag film is about 0.06 or smaller.

[0261] That is, in order to achieve an improved TCF, a largeelectromechanical coupling coefficient, and a small attenuationconstant, it is necessary to suitably combine the cut angle of a LiTaO₃substrate, the thickness of a SiO₂ film, and the thickness of an Agfilm.

[0262]FIGS. 40 through 47 illustrate the relationship between theattenuation constant α and θ of the Euler angles when Ag films having anormalized thickness H/λ of about 0.1 or smaller were formed on a LiTaO₃substrate and when the normalized thickness Hs/λ of the SiO₂ film waschanged to about 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, and 0.45,respectively.

[0263] As is seen from FIGS. 40 through 47, by setting the thickness ofthe Ag film to be about 0.01 to about 0.08 and by selecting any of thefollowing combinations of the SiO₂ film and Θ of the Euler angles shownin the center column of table Table 3, it is possible to implement ahigh level of TCF, a large electromechanical coupling coefficient, and asmall attenuation constant α. It is more preferable that the Eulerangles on the right side of table are selected In which case, superiorcharacteristics are obtained. TABLE 3 Ag thickness H/λ: about 0.01 toabout 0.08 SiO₂ thickness Euler angles of More preferable Hs/λ LiTaO₃(°) Euler angles (°) 0.15-0.18 0 ± 3, 117-137, 0 ± 3 0 ± 3, 120-135, 0 ±3 0.18-0.23 0 ± 3, 117-136, 0 ± 3 0 ± 3, 118-133, 0 ± 3 0.23-0.28 0 ± 3,115-135, 0 ± 3 0 ± 3, 117-133, 0 ± 3 0.28-0.33 0 ± 3, 113-133, 0 ± 3 0 ±3, 115-132, 0 ± 3 0.33-0.38 0 ± 3, 113-135, 0 ± 3 0 ± 3, 115-133, 0 ± 30.38-0.40 0 ± 3, 113-132, 0 ± 3 0 ± 3, 115-130, 0 ± 3

[0264] When the normalized thickness H/λ of the Ag film is about 0.02 toabout 0.06, any of the following combinations shown in Table 4 of thenormalized thickness of the SiO₂ film and Θ of the Euler angles in thecenter column, and more preferable Euler angles on the right side ofTable 4, in which case superior characteristics are obtained, can beselected. TABLE 4 Ag thickness H/λ: about 0.02 to about 0.06 SiO₂thickness Euler angles of More preferable Hs/λ LiTaO₃ (°) Euler angles(°) 0.15-0.18 0 ± 3, 120-133, 0 ± 3 0 ± 3, 122-130, 0 ± 3 0.18-0.23 0 ±3, 120-137, 0 ± 3 0 ± 3, 122-136, 0 ± 3 0.23-0.28 0 ± 3, 120-135, 0 ± 30 ± 3, 122-133, 0 ± 3 0.28-0.33 0 ± 3, 118-135, 0 ± 3 0 ± 3, 120-133, 0± 3 0.33-0.38 0 ± 3, 115-133, 0 ± 3 0 ± 3, 117-130, 0 ± 3 0.38-0.40 0 ±3, 113-130, 0 ± 3 0 ± 3, 115-128, 0 ± 3

[0265] When the standard thickness H/λ of the Ag film is about 0.03 toabout 0.05, any of the following combinations shown in Table 5 of thethickness of the SiO₂ film and Θ of the Euler angles in the centercolumn, and more preferable Euler angles on the right side of Table 5,in which case superior results are obtained, can be selected. TABLE 5 Agthickness H/λ: about 0.03 to about 0.05 SiO₂ thickness Euler angles ofMore preferable Hs/λ LiTaO₃ (°) Euler angles (°) 0.15-0.18 0 ± 3,122-142, 0 ± 3 0 ± 3, 123-140, 0 ± 3 0.18-0.23 0 ± 3, 120-140, 0 ± 3 0 ±3, 122-137, 0 ± 3 0.23-0.28 0 ± 3, 117-138, 0 ± 3 0 ± 3, 120-135, 0 ± 30.28-0.33 0 ± 3, 116-136, 0 ± 3 0 ± 3, 118-134, 0 ± 3 0.33-0.38 0 ± 3,114-135, 0 ± 3 0 ± 3, 117-133, 0 ± 3 0.38-0.40 0 ± 3, 113-130, 0 ± 3 0 ±3, 115-128, 0 ± 3

[0266] In preferred embodiments of the present invention, the IDT may bemade of only Ag Alternatively, the IDT may be made of an Ag alloy or alaminated electrode of Ag and another metal, as long as such an alloy ora laminated electrode primarily comprises Ag. In this case, it ispreferably that Ag constitutes about 80% by weight of the total IDT.Accordingly, an Al thin film or a Ti thin film may be formed as anunderlying layer of the Ag IDT. In this case, it is preferable that Agconstitutes about 80% by weight of the total of the underlying layer andthe IDT.

[0267] In the above-described example, a LiTaO₃ substrate having Eulerangles (0°, Θ, 0°) was used, and normally, there is a variation of 0±3°in φ and ψ. However, even in a LiTaO₃ substrate having such a variation,i.e., (0±3°, 113°-142°, 0±3°), advantages of the preferred embodimentsof the present invention can be achieved.

[0268] Euler angle Θ may sometimes deviate from the desired angle byabout −2° to about +4°. This deviation is generated caused by the factthat calculations were made in this preferred embodiment assuming that ametallic film was formed on the entire surface of the substrate, andthere may be some errors within the above range in actual SAWapparatuses.

[0269] A SAW apparatus of a fourth preferred embodiment of the presentinvention is described below. The SAW apparatus of the fourth preferredembodiment of the present invention is similar to the SAW apparatus 21of the second preferred embodiment of the present invention shown inFIG. 15, except that the IDTs 23 a and 23 b are made of Cu. Because theelectrodes are made of Cu having a higher density than Al, theelectromechanical coupling coefficient and the reflection coefficientare improved.

[0270]FIG. 58 illustrates the relationship between the reflectioncoefficient of a Cu electrode and that of an Al electrode and thethickness of the corresponding electrode when the normalized thicknessof a SiO₂ film is about 0.20.

[0271]FIG. 58 shows that the reflection coefficient per electrode fingercan be increased when a Cu electrode was used rather than an Alelectrode. In this case, the number of electrode fingers can bedecreased. Thus, the size of the reflectors can be reduced, andaccordingly, the overall size of the resulting SAW apparatus can bereduced.

[0272] As discussed below, the thickness H/λ of the IDTs 23 a and 23 bstandardized by the wavelength λ is preferably from about 0.01 to about0.08.

[0273]FIG. 48 illustrates a change in the attenuation constant α when Cuelectrodes having a normalized thickness of H/λ of about 0.10 or smallerand SiO₂ films having a normalized thickness Hs/λ of 0 to about 0.5 wereformed on a LiTaO₃ substrate having Euler angles (0°, 120°, 0°). FIG. 48shows that the attenuation constant α is small when the thickness Hs/λof the SiO₂ film is about 0.2 to about 0.4 and when the thickness H/λ ofthe Cu film is about 0.01 to about 0.10.

[0274]FIG. 49 illustrates a change in the attenuation constant α when Cuelectrodes having a normalized thickness of H/λ of 0 to about 0.10 andSiO₂ films having a normalized thickness Hs/λ of 0 to about 0.5 wereformed on a LiTaO₃ substrate having Euler angles (0°, 135°, 0°). As isseen from FIG. 49, when Θ is 135°, the attenuation constant α becomeslarger as the normalized thickness of the Cu film decreases and thenormalized thickness of the SiO₂ film increases.

[0275] Accordingly, in order to achieve an improved TCF, a largeelectromechanical coupling coefficient, and a small attenuationconstant, it is necessary to suitably combine the cut angles of a LiTaO₃substrate, the thickness of a SiO₂ film, and the thickness of a Cuelectrode.

[0276]FIGS. 50 through 57 illustrate the relationship between theattenuation constant α and Θ of the Euler angles when the Cu filmshaving a normalized thickness H/λ of about 0.1 or smaller were formed ona LiTaO₃ substrate and when the normalized thickness Hs/λ of the SiO₂film was changed to about 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, and0.45, respectively.

[0277] As is seen from FIGS. 50 through 57, by setting the thickness H/λof the Cu film to be about 0.01 to about 0.08 and by selecting any ofthe following combinations of the SiO₂ film and Θ of the Euler anglesshown in the center column of Table 6, it is possible to implement animproved TCF (±20 ppm/° C.), a large electromechanical couplingcoefficient, and a small attenuation constant α. More preferable, Eulerangles shown on the right side of Table 6 are selected. In which case,superior characteristics are obtained. TABLE 6 SiO₂ thickness Eulerangles of More preferable Hs/λ LiTaO₃ (°) Euler angles (°) 0.15-0.18 0 ±3, 117-137, 0 ± 3 0 ± 3, 120-135, 0 ± 3 0.18-0.23 0 ± 3, 117-136, 0 ± 30 ± 3, 118-133, 0 ± 3 0.23-0.28 0 ± 3, 115-135, 0 ± 3 0 ± 3, 117-133, 0± 3 0.28-0.33 0 ± 3, 113-133, 0 ± 3 0 ± 3, 115-132, 0 ± 3 0.33-0.38 0 ±3, 113-135, 0 ± 3 0 ± 3, 115-133, 0 ± 3 0.38-0.40 0 ± 3, 113-132, 0 ± 30 ± 3, 115-130, 0 ± 3

[0278] As can be inferred from the electromechanical couplingcoefficient K_(SAW) when the Au electrode was used shown in FIG. 25, theelectromechanical coupling coefficient K_(SAW) is considerably increasedwhen Θ of the Euler angle is about 125° or smaller. Accordingly, it ismore preferable that the combinations of the normalized thickness Hs/λof the SiO₂ film and the Euler angles shown in Table 7 are selected.TABLE 7 SiO₂ thickness Euler angles of Hs/λ LiTaO₃ (°) 0.15-0.18 0 ± 3,117-125, 0 ± 3 0.18-0.23 0 ± 3, 117-125, 0 ± 3 0.23-0.28 0 ± 3, 115-125,0 ± 3 0.28-0.33 0 ± 3, 113-125, 0 ± 3 0.33-0.38 0 ± 3, 113-125, 0 ± 30.38-0.40 0 ± 3, 113-125, 0 ± 3

[0279] The Euler angle Θ_(min) that reduces the attenuation constant αto substantially 0 or minimizes the attenuation constant α with respectto the normalized thickness Hs/λ of the SiO₂ film and the normalizedthickness H/λ of the Cu film was determined from the results of FIGS. 48through 56. Such an Euler angle Θ_(min) is shown in FIG. 59.

[0280] By approximating the curves shown in FIG. 59 with a cubicpolynomial when the normalized thickness H/λ of the Cu film isapproximately 0, 0.02, 0.04, 0.06, and 0.08, the following equations Athrough E were found:

[0281] (a) When 0<H/λ≦0.01

Θ_(min)=−139.713×Hs ³+43.07132×Hs ²−20.568011×Hs+125.8314  A

[0282] (b) When 0.01<H/λ≦0.03

Θ_(min)=−139.660×Hs ³+46.02985×Hs ²−21.141500×Hs+127.4181  B

[0283] (c) When 0.03<H/λ≦0.05

Θ_(min)=−139.607×Hs ³+48.98838×Hs ²−21.714900×Hs+129.0048  C

[0284] (d) When 0.05<H/λ≦0.07

Θ_(min)−112.068×Hs3+39.60355×Hs ²−21.186000×Hs+129.9397  D

[0285] (e) When 0.07<H/λ≦0.09

Θ_(min)=−126.954×Hs ³+67.40488×Hs ²−29.432000×Hs+131.5686  E

[0286] Accordingly, it is preferable that Θ of the Euler angles (0±3°,Θ, 0±3°) is Θ_(min) determined by the above-described equations Athrough E. However, when Θ_(min)−2°<Θ≦Θ_(min)+2°, the attenuationconstant can be effectively decreased.

[0287] In preferred embodiments of the present invention, the IDT may bemade of only Cu. Alternatively, the IDT may be made of a Cu alloy or alaminated electrode of Cu and another metal, as long as such an alloy ora laminated electrode primarily comprises Cu. More specifically, the IDTprimarily including Cu preferably satisfies the following condition whenthe average density of the electrode is indicated by

(average):

(Cu)×0.7≦

(average)≦

(Cu)×1.3,

i.e., 6.25 g/cm ³≦

(average)≦11.6 g/cm ³.

[0288] An upper layer or an underlying layer made of a metal having adensity higher than Al, such as W, Ta, Au, Pt, Ag, or Cr, may belaminated on the Cu electrode so that

(average) satisfies the above-described condition. In this case,advantages similar to those obtained by a single Cu layer can beachieved.

[0289] Θ of the Euler angles may sometimes deviate from the desiredangle by about −2° to about +4°. This deviation is caused by the factthat calculations were made in this preferred embodiment assuming that ametallic film was formed on the entire surface of the substrate, andthere may be some errors within the above range in actual SAWapparatuses.

[0290] When manufacturing SAW apparatuses, there is a variation of about0±3° in φ and ψ of the Euler angles. However, substantially the samecharacteristic as that when φ and Ψ are 0° can be obtained.

[0291] A SAW apparatus of a fifth preferred embodiment of the presentinvention is described below. The SAW apparatus of the fifth preferredembodiment of the present invention is similar to the SAW apparatus 21of the second preferred embodiment of the present invention shown inFIG. 15, except that the IDTs 23 a and 23 b and the reflectors 24 a and24 b are made of tungsten (W). The normalized thickness H/λ of the IDTsis about 0.0025 to about 0.06.

[0292] As the piezoelectric substrate 22, a 22°-48°-rotated Y-plateX-propagating LiTaO₃ substrate having Euler angles (0°, 112°-138°, 0°)was used.

[0293] In the fifth preferred embodiment of the present invention,because the 22°-48°-rotated Y-plate X-propagating LiTaO₃ substrate 22,the IDTs 23 a and 23 b made of tungsten having a thickness H/λ of about0.0025 to about 0.06, and the SiO₂ film 25 having a thickness Hs/λ ofabout 0.10 to about 0.40 were used, it is possible to provide a SAWapparatus that has an improved TCF, a large electromechanical couplingcoefficient K_(SAW), and a small propagation loss. The fifth preferredembodiment of the present invention is described in detail below by wayof a specific example.

[0294]FIGS. 60 and 61 illustrate a change in the attenuation constant αwhen tungsten IDTs having different thickness values and SiO₂ filmshaving different thickness values were formed on a LiTaO₃ substratehaving Euler angles (0°, 120°, 0°) and a LiTaO₃ substrate having Eulerangles (0°, 140°, 0°), respectively.

[0295] As is seen from FIG. 60, when Θ is 120°, the attenuation constantα is small when the thickness Hs/λ of the SiO₂ film is about 0.1 toabout 0.4 and the thickness H/λ of the tungsten electrode is about 0.0to about 0.10. As is seen from FIG. 61, when Θ is 140°, the attenuationconstant α increases as the thickness H/λ of the tungsten electrodechanges from 0.0 to about 0.10, regardless of the thickness Hs/λ of theSiO₂ film.

[0296] In order to reduce the TCF to be between about −20 ppm/° C. andabout +20 ppm/° C., to achieve a large electromechanical couplingcoefficient, and to decrease the attenuation constant, the Euler anglesof the LiTaO₃ substrate, the thickness of the SiO₂ film, and thethickness of the tungsten electrode, must be considered.

[0297]FIGS. 62 through 65 illustrate the relationship between theattenuation constant α and Θ of the Euler angles when the normalizedthickness Hs/λ of the SiO₂ film and the normalized thickness H/λ of thetungsten electrode were changed.

[0298] As is seen from FIGS. 62 through 65, optimal combinations of thenormalized thickness of the SiO₂ film and the Euler angle O, when thenormalized thickness H/λ of the tungsten electrode is about 0.012 toabout 0.053 and, more preferably, is about 0.015 to about 0.042, can beselected from the combinations shown in Table 8 and Table 9,respectively. Euler angle Θ shown in Table 8 and Table 9 may vary byabout −2° to about +4° due to a variation in the electrode finger widthof the tungsten electrode or a variation in the single crystalsubstrate. The thickness values which are not shown in FIGS. 62 through65 are determined by the proportional distribution. TABLE 8 Tungstenthickness H/λ: about 0.012 to about 0.053 SiO₂ thickness Euler angles ofLiTaO₃ More preferable Euler Hs/λ (°) angles (°) 0.10-0.15 0 ± 3,114.2-138.0, 0 ± 3 0 ± 3, 117.7-134.0, 0 ± 3 0.15-0.20 0 ± 3,113.0-137.8, 0 ± 3 0 ± 3, 117.0-133.5, 0 ± 3 0.20-0.30 0 ± 3,113.0-137.5, 0 ± 3 0 ± 3, 116.5-133.0, 0 ± 3 0.30-0.35 0 ± 3,112.7-137.0, 0 ± 3 0 ± 3, 116.5-133.0, 0 ± 3 0.35-0.40 0 ± 3,112.5-136.0, 0 ± 3 0 ± 3, 116.5-132.3, 0 ± 3

[0299] TABLE 9 Tungsten thickness H/λ: about 0.015 to about 0.042 SiO₂thickness Euler angles of LiTaO₃ More preferable Euler (Hs/λ) (°) angles(°) 0.10-0.15 0 ± 3, 114.3-138.0, 0 ± 3 0 ± 3, 117.7-133.5, 0 ± 30.15-0.20 0 ± 3, 113.0-137.5, 0 ± 3 0 ± 3, 117.7-133.5, 0 ± 3 0.20-0.300 ± 3, 112.5-137.0, 0 ± 3 0 ± 3, 117.0-132.5, 0 ± 3 0.30-0.35 0 ± 3,112.2-136.5, 0 ± 3 0 ± 3, 116.8-132.5, 0 ± 3 0.35-0.40 0 ± 3,112.0-135.3, 0 ± 3 0 ± 3, 116.0-131.5, 0 ± 3

[0300] When the normalized thickness H/λ of the tungsten electrode isabout 0.012 to about 0.053, as indicated in Table 8, the normalizedthickness Hs/λ of the SiO₂ film is preferably about 0.1 to about 0.4 inorder to set the range of the TCF to be between about −20 ppm/° C. andabout +20 ppm/° C. In this case, Euler angle Θ of the LiTaO₃ substrateis preferably between about 112° and about 138° (corresponding to therotation angle of about 20° to about 50°), More preferably, the Eulerangles indicated on the right side of Table 8 are selected.

[0301] Similarly, when the normalized thickness H/λ of the tungstenelectrode is about 0.015 to about 0.042, as indicated in Table 9, thenormalized thickness Hs/λ of the SiO₂ film is preferably about 0.1 toabout 0.4 in order to set the range of the TCF to be between about − andabout +20 ppm/° C. In this case, Θ of the Euler angles of the LiTaO₃substrate is preferably between about 112° and about 138°. Morepreferably, the Euler angles indicated on the right side of Table 9 areselected.

[0302] The Euler angles of LiTaO₃ shown in Table 8 and Table 9 wereselected so that the attenuation constant becomes about 0.05 or lower.The more preferable Euler angles shown in Table 8 and Table 9 wereselected so that the attenuation constant becomes about 0.025 or lower.The relationships between the Hs/λ of the SiO₂ film and the Euler anglesshown in Table 8 and Table 9 when the thickness H/λ of the tungstenelectrode is approximately 0.012, 0.015, 0.042, and 0.053 weredetermined in terms of the thickness H/λ of the tungsten electrode shownin FIGS. 62 through 65.

[0303] When manufacturing the SAW apparatus of this preferredembodiment, it is preferable that an IDT primarily including tungsten isformed on a rotated Y-plate X-propagating LiTaO₃ substrate. Then, thefrequency is adjusted. Then, a SiO₂ film having a thickness that canreduce the attenuation constant α is formed. This is explained belowwith reference to FIGS. 66 and 67. Tungsten IDTs having differentthickness values and SiO₂ films having different thickness values wereformed on a rotated Y-plate X-propagating LiTaO₃ substrate (Euler angles(0°, 126°, 0°)). FIG. 66 illustrates a change in the acoustic velocityof a leaky SAW with respect to the thickness of the SiO₂ film. FIG. 67illustrates a change in the acoustic velocity of a leaky SAW withrespect to the thickness of the tungsten electrode. FIGS. 66 and 67 showthat a change in the acoustic velocity of the SAW is much larger whenthe thickness of the tungsten IDT is varied than when the thickness ofthe SiO₂ film is varied. Accordingly, it is desirable that the frequencyis adjusted before the formation of the SiO₂ film. It is desirable thatthe frequency is adjusted after a tungsten IDT is formed by laseretching or ion etching.

[0304] In this preferred embodiment, a 22°-48°-rotated Y-plateX-propagating LiTaO₃ substrate having Euler angles (0°, 112°-138°, 0°),a tungsten IDT having a thickness H/λ of about 0.0025 to about 0.06, anda SiO₂ film having a thickness Hs/λ of about 0.10 to about 0.40 areused. The number and the structure of IDTs are not particularlyrestricted. That is, the present invention can be applied to, not onlythe SAW apparatus shown in FIG. 15, but also various types of SAWresonators and SAW filters as long as the above-described conditions aresatisfied.

[0305] Euler angles Θ may sometimes deviate from the desired angle byabout −2° to about +4°. This deviation is caused by the fact thatcalculations were made in this embodiment assuming that a metallic filmwas formed on the entire surface of the substrate, and there may be someerrors within the above range in actual SAW apparatuses.

[0306] When manufacturing SAW apparatuses, although φ and ψ of the Eulerangles deviate from 0° by ±3°, substantially the same characteristic asthat when φ and ψ are 0° can be obtained.

[0307] A SAW apparatus of a sixth preferred embodiment of the presentinvention is described below. The SAW apparatus of the sixth preferredembodiment of the present invention is similar to the SAW apparatus 21of the second preferred embodiment of the present invention shown inFIG. 15. However, as the piezoelectric substrate 22, a 14°-58°-rotatedY-plate X-propagating LiTaO₃ substrate having Euler angles (0°,104°-148°, 0°) was used, and IDTs made of tantalum (Ta) having thethickness H/λ of about 0.004 to about 0.055 were used.

[0308] In the sixth preferred embodiment, because a 14°-58°-rotatedY-plate X-propagating LiTaO₃ substrate 22 having Euler angles (0°,104°-148°, 0°), IDTs 23 a and 23 b made of tantalum having a thicknessH/λ of about 0.004 to about 0.055, and a SiO₂ film 25 having a thicknessHs/λ of about 0.10 to about 0.40 were used, it is possible to provide aSAW apparatus that has an improved TCF, a large electromechanicalcoupling coefficient K_(SAW), and a small propagation loss. The sixthpreferred embodiment of the present invention is described in detailbelow by way of a specific example.

[0309]FIGS. 68 and 69 illustrate a change in the attenuation constant αwhen tantalum IDTs having different thickness values and SiO₂ filmshaving different thickness values were formed on a LiTaO₃ substratehaving Euler angles (0°, 120°, 0°) and a LiTaO₃ substrate having Eulerangles (0°, 140°, 0°).

[0310] As is seen from FIG. 68, when Θ is 120°, the attenuation constantα is small when the thickness Hs/λ of the SiO₂ film is about 0.1 toabout 0.4 and when the thickness H/λ of the tantalum electrode is about0.0 to about 0.1. In contrast, as is seen from FIG. 69, when Θ is 140°,the attenuation constant α is large TABLE 10 Tantalum thickness H/λ:about 0.01 to about 0.055 SiO₂ thickness Euler angles of LiTaO₃ Morepreferable Euler Hs/λ (°) angles (°) 0.10-0.15 0 ± 3, 110.5-148.0, 0 ± 30 ± 3, 116.0-143.0, 0 ± 3 0.15-0.20 0 ± 3, 108.0-147.5, 0 ± 3 0 ± 3,115.0-141.5, 0 ± 3 0.20-0.30 0 ± 3, 105.0-148.0, 0 ± 3 0 ± 3,111.0-139.0, 0 ± 3 0.30-0.35 0 ± 3, 104.5-148.0, 0 ± 3 0 ± 3,111.0-139.0, 0 ± 3 0.35-0.40 0 ± 3, 104.0-145.0, 0 ± 3 0 ± 3,110.0-138.5, 0 ± 3

[0311] TABLE 11 Tantalum thickness H/λ: about 0.016 to about 0.045 SiO₂thickness Euler angles of LiTaO₃ More preferable Euler (Hs/λ) (°) angles(°) 0.10-0.15 0 ± 3, 113.0-144.0, 0 ± 3 0 ± 3, 118.0-140.0, 0 ± 30.15-0.20 0 ± 3, 111.0-144.0, 0 ± 3 0 ± 3, 117.0-139.5, 0 ± 3 0.20-0.300 ± 3, 108.0-144.0, 0 ± 3 0 ± 3, 113.0-139.0, 0 ± 3 0.30-0.35 0 ± 3,107.5-143.0, 0 ± 3 0 ± 3, 112.5-137.0, 0 ± 3 0.35-0.40 0 ± 3,107.0-140.5, 0 ± 3 0 ± 3, 112.0-135.5, 0 ± 3

[0312] When the thickness H/λ of the tantalum electrode is about 0.01 toabout 0.055, as indicated in Table 10, the thickness Hs/λ of the SiO₂film is preferably about 0.1 to about 0.4 in order to set the range ofthe TCF to between about −20 ppm/° C. and about +20 ppm/° C. In thiscase, Euler angle Θ of the LiTaO₃ substrate are preferably between about104° and about 148° (corresponding to the rotation angle of about 14° toabout 58°), and more preferably, the Euler angles indicated on the rightside of Table 10 are selected according to the thickness Hs/λ of theSiO₂ film.

[0313] Similarly, when the thickness H/λ of the tantalum electrode isabout 0.016 to about 0.045, as indicated in Table 11, the thickness Hs/λof the SiO₂ film is preferably about 0.1 to about 0.4 in order toimprove the TCF. In this case, Euler angle Θ of the LiTaO₃ substrate ispreferably between about 107° and about 144°, and more preferably, theEuler angles indicated on the right side of Table 11 are selectedaccording to the thickness of the SiO₂ film.

[0314] The Euler angles of LiTaO₃ shown in Table 10 and Table 11 wereselected so that the attenuation constant becomes about 0.05 or lower.The more preferable Euler angles shown in Table 10 and Table 11 wereselected so that the attenuation constant becomes about 0.025 or lower.The relationships between the Hs/λ of the SiO₂ film and the Euler anglesshown in Table 10 and Table 11 when the thickness H/λ of the tantalumelectrode is about 0.012, 0.015, 0.042, and 0.053 were determined interms of the thickness H/λ of the tantalum electrode shown in FIGS. 70through 73.

[0315] When manufacturing the SAW apparatus of this preferredembodiment, it is preferable that an IDT primarily including tantalum isformed on a rotated Y-plate X-propagating LiTaO₃ substrate. Then, thefrequency is adjusted Then, a SiO₂ film having a thickness that reducesthe attenuation constant α is formed. This is explained below withreference to FIGS. 74 and 75. Tantalum IDTs having different thicknessvalues and SiO₂ films having different thickness values were formed on arotated Y-plate X-propagating LiTaO₃ substrate (Euler angles (0°, 126°,0°)). FIG. 74 illustrates a change in the acoustic velocity of a leakySAW with respect to the thickness of the SiO₂ film. FIG. 75 illustratesa change in the acoustic velocity of a leaky SAW with respect to thethickness of the tantalum electrode. FIGS. 74 and 75 show that a changein the acoustic velocity of the SAW is much larger when the thickness ofthe tantalum IDT is varied than when the thickness of the SiO₂ film isvaried. Accordingly, it is desirable that the frequency is adjustedbefore the formation of the SiO₂ film. It is desirable that thefrequency is adjusted after a tantalum IDT is formed by laser etching orion etching.

[0316] In this preferred embodiment, as described above, a14°-58°-rotated Y-plate X-propagating LiTaO₃ substrate having Eulerangles (0°, 104°-148°, 0°), a tantalum IDT having a thickness H/λ ofabout 0.004 to about 0.055, and a SiO₂ film having a thickness Hs/λ ofabout 0.10 to about 0.40 are used. The number and the structure of IDTsare not particularly restricted. That is, the present invention can beapplied to, not only the SAW apparatus shown in FIG. 15, but alsovarious types of SAW resonators and SAW filters as long as theabove-described conditions are satisfied.

[0317] Euler angle Θ may sometimes deviate from the desired angle byabout −2° to about +4°. This deviation is caused by the fact thatcalculations were made in this preferred embodiment assuming that ametallic film was formed on the entire surface of the substrate, andthere may be some errors within the above range in actual SAWapparatuses.

[0318] When manufacturing SAW apparatuses, although φ and ψ of the Eulerangles deviate from 0° by ±30, substantially the same characteristic asthat when φ and ψ are 0° can be obtained.

[0319] A SAW apparatus of a seventh preferred embodiment of the presentinvention is described below. The SAW apparatus of the seventh preferredembodiment of the present invention is similar to the SAW apparatus 21of the second preferred embodiment of the present invention shown inFIG. 15. However, as the piezoelectric substrate 22, a 0°-79°-rotatedY-plate X-propagating LiTaO₃ substrate having Euler angles (0°,90°-169°, 0°) was used, and IDTs made of platinum having a thickness H/λof about 0.005 to about 0.054 were used.

[0320] In the seventh preferred embodiment, because the 0°-79° -rotatedY-plate X-propagating LiTaO₃ substrate 22 having Euler angles (0°,90°-169°, 0°), the IDTs 23 a and 23 b made of platinum having athickness H/λ of about 0.005 to about 0.054, and the SiO₂ film 25 havinga thickness Hs/λ of about 0.10 to about 0.40 were used, it is possibleto provide a SAW apparatus that has an improved TCF, a largeelectromechanical coupling coefficient K_(SAW), and a small propagationloss. The seventh preferred embodiment of the present invention isdescribed in detail below by way of a specific example.

[0321]FIGS. 76 and 77 illustrate a change in the attenuation constant αwhen platinum IDTs having different thickness values and SiO₂ filmshaving different thickness values were formed on a LiTaO₃ substratehaving Euler angles (0°, 125°, 0°) and a LiTaO₃ substrate having Eulerangles (0°, 140°, 0°).

[0322] As is seen from FIG. 76, when Euler angle Θ is 125°, theattenuation constant α is small when the normalized thickness Hs/λ ofthe SiO₂ film is about 0.1 to about 0.4 and when the normalizedthickness H/λ of the platinum electrode is about 0.005 to about 0.06. Incontrast, as is seen from FIG. 77, when Θ is 140°, the attenuationconstant α is large when the normalized thickness H/λ of the platinumelectrode is about 0.005 to about 0.06 regardless of the thickness Hs/λof the SiO₂ film.

[0323] That is, in order to decrease the absolute value of the TCF, toachieve a large electromechanical coupling coefficient, and to decreasethe attenuation constant, the Euler angles of the LiTaO₃ substrate, thethickness of the SiO₂ film, and the thickness of the platinum electrodemust be considered.

[0324]FIGS. 78 and 83 illustrate relationships between the attenuationconstant α and Euler angle Θ when the normalized thickness Hs/λ of theSiO₂ film and the normalized thickness H/λ of the platinum electrodewere changed.

[0325] As is seen from FIGS. 78 through 83, it is desirable that Θ isfrom 90° to 169° when the thickness H/λ of the platinum electrode isabout 0.005 to about 0.054. Combinations of the TABLE 13 Platinumthickness H/λ: about 0.013 to about 0.033 SiO₂ thickness Euler angles ofMore preferable Euler Hs/λ LiTaO₃ (°) angles (°) 0.10 ≦ Hs/λ < 0.15 0 ±3, 106-155, 0 ± 3 0 ± 3, 116.0-147.5, 0 ± 3 0.15 ≦ Hs/λ < 0.20 0 ± 3,104-155, 0 ± 3 0 ± 3, 113.5-150.0, 0 ± 3 0.20 ≦ Hs/λ < 0.25 0 ± 3,102-155, 0 ± 3 0 ± 3, 111.5-150.0, 0 ± 3 0.25 ≦ Hs/λ < 0.30 0 ± 3,102-154, 0 ± 3 0 ± 3, 35 U.S.C. §112, .0-146.0, 0 ± 3 0.30 ≦ Hs/λ < 0.400 ± 3, 102-153, 0 ± 3 0 ± 3, 110.0-144.5, 0 ± 3

[0326] When the thickness H/λ of the platinum electrode is about 0.01 toabout 0.04, as indicated in Table 12, the thickness Hs/λ of the SiO₂film is preferably 0.1 to 0.4 in order to set the range of the TCF to bebetween about −20 ppm/° C. and about +20 ppm/° C. In this case, Eulerangle Θ of the LiTaO₃ substrate is preferably 90° to 169° (correspondingto the rotation angle of 0° to 79°), and more preferably, the Eulerangles indicated on the right side of Table 12 are selected according tothe thickness Hs/λ of the SiO₂ film.

[0327] Similarly, when the thickness H/λ of the platinum electrode isabout 0.013 to about 0.033, as indicated in Table 13, the thickness Hs/λof the SiO₂ film is preferably about 0.1 to about 0.4 in order to setthe range of the TCF to be between about −20 ppm/° C. and about +20ppm/° C. In this case, Euler angle Θ of the LiTaO₃ substrate ispreferably 102° to 155°, and more preferably, the Euler angles shown onthe right side of Table 13 are selected according to the thickness ofthe SiO₂ film.

[0328] The relationships between the Hs/λ of the SiO₂ film and the Eulerangles shown in Table 12 and Table 13 when the thickness H/λ of theplatinum electrode is from about 0.013 to about 0.033 were determined interms of the thickness H/λ of the platinum electrode shown in FIGS. 78through 83.

[0329] When manufacturing the SAW apparatus of this preferredembodiment, it is preferable that an IDT primarily including platinum isformed on a rotated Y-plate X-propagating LiTaO₃ substrate. Then, thefrequency is adjusted. Then, a SiO₂ film having a thickness that canreduce the attenuation constant α is formed. This is explained belowwith reference to FIGS. 84 and 85. Platinum IDTs having differentthickness values and SiO₂ films having different thickness values wereformed on a rotated Y-plate X-propagating LiTaO₃ substrate (Euler angles(0°, 126°, 0°)). FIG. 84 illustrates a change in the acoustic velocityof a leaky SAW with respect to the thickness of the SiO₂ film. FIG. 85illustrates a change in the acoustic velocity of a leaky SAW withrespect to the thickness of the platinum electrode. FIGS. 84 and 85 showthat a change in the acoustic velocity of the SAW is much larger whenthe thickness of the platinum IDT is varied than when the thickness ofthe SiO₂ film is varied. Accordingly, it is desirable that the frequencyis adjusted before the formation of the SiO₂ film. It is desirable thatthe frequency is adjusted after a platinum IDT is formed by laseretching or ion etching.

[0330] In this preferred embodiment, a 0°-79°-rotated Y-plateX-propagating LiTaO₃ substrate having Euler angles (0°, 90°-169°, 0°), aplatinum IDT having a thickness H/λ of about 0.005 to about 0.054, and aSiO₂ film having a thickness Hs/λ of about 0.10 to about 0.40 are used.The number and the structure of IDTs are not particularly restricted.That is, the present invention can be applied to, not only the SAWapparatus shown in FIG. 15, but also various types of SAW resonators andSAW filters as long as the above-described conditions are satisfied.

[0331] A SAW apparatus of an eighth preferred embodiment of the presentinvention is described below. The SAW apparatus of the eighth preferredembodiment of the present invention is similar to the SAW apparatus 21of the second preferred embodiment of the present invention shown inFIG. 15. However, as the piezoelectric substrate 22, a 14°-50°-rotatedY-plate X-propagating LiTaO₃ substrate having Euler angles (0°,104°-140°, 0°) was used, and electrodes made of nickel (Ni) ormolybdenum (Mo) were used.

[0332] The IDTs 23 a and 23 b and the reflectors 24 a and 24 b are madeof a metal having a density of about 8700 to about 10300 kg/m³, aYoung's modulus of about 1.8×10¹¹ to about 4×10¹¹ N/m², and atransversal-wave acoustic velocity of about 3170 to about 3290 m/s. Sucha metal includes nickel, molybdenum, or an alloy primarily includingnickel or molybdenum. The normalized thickness H/λ of the IDTs 23 a and23 b ranges from about 0.008 to about 0.06.

[0333] In the eighth preferred embodiment of the present invention,since the 14°-50°-rotated Y-plate X-propagating LiTaO₃ substrate 22having Euler angles (0°, 104°-140°, 0°), the IDTs 23 a and 23 b made ofthe above-described type of metal having a normalized thickness H/λ ofabout 0.008 to about 0.06, and the SiO₂ film 25 having a normalizedthickness Hs/λ of about 0.10 to about 0.40 were used, it is possible toprovide a SAW apparatus that has an improved TCF, a largeelectromechanical coupling coefficient K_(SAW), and a small propagationloss. The eighth preferred embodiment of the present invention isdescribed in detail below by way of a specific example.

[0334]FIGS. 86 and 87 illustrate a change in the attenuation constant αwhen nickel IDTs having different thickness values and SiO₂ films havingdifferent thickness values were formed on a LiTaO₃ substrate havingEuler angles (0°, 120°, 0°) and a LiTaO₃ substrate having Euler angles(0°, 140°, 0°).

[0335] As is seen from FIG. 86, when Euler angle Θ is about 120°, theattenuation constant α is small when the normalized thickness Hs/λ ofthe SiO₂ film is about 0.1 to about 0.4 and when the normalizedthickness H/λ of the nickel electrode is about 0.008 to about 0.08. Incontrast, as is seen from FIG. 87, when Θ is about 140°, the attenuationconstant α is large when the thickness H/λ of the nickel electrode isabout 0.008 to about 0.08 regardless of the normalized thickness Hs/λ ofthe SiO₂ film.

[0336]FIGS. 88 and 89 illustrate a change in the attenuation constant αwhen molybdenum IDTs having different thickness values and SiO₂ filmshaving different thickness values were formed on a LiTaO₃ substratehaving Euler angles (00, 1200, 00) and a LiTaO₃ substrate having Eulerangles (0°, 140°, 0°).

[0337] As is seen from FIG. 88, when Euler angle Θ is about 120°, theattenuation constant α is small when the normalized thickness Hs/λ ofthe SiO₂ film is about 0.1 to about 0.4 and when the normalizedthickness H/λ of the molybdenum electrode is about 0.008 to about 0.08.In contrast, as is seen from FIG. 89, when Euler angle Θ is about 140°,the attenuation constant α is large when the thickness H/λ of themolybdenum electrode is about 0.008 to about 0.08 regardless of thenormalized thickness Hs/λ of the SiO₂ film.

[0338] That is, in order to decrease the absolute value of the TCF, toachieve a large electromechanical coupling coefficient, and to decreasethe attenuation constant, the Euler angles of the LiTaO₃ substrate, thethickness of the SiO₂ film, and the thickness of a metal having theabove-described density, the Young's modulus, and the transversal-waveacoustic velocity must be considered.

[0339]FIGS. 90 through 93 illustrate the relationships between theattenuation constant α and Euler angle Θ when the normalized thicknessHs/λ of the SiO₂ film and the normalized thickness H/λ of the nickelelectrode are changed.

[0340]FIGS. 94 through 97 illustrate the relationships between theattenuation constant α and Euler angle Θ when the normalized thicknessHs/λ of the SiO₂ film and the normalized thickness H/λ of the molybdenumelectrode are changed.

[0341] As is seen from FIGS. 90 through 97, optimal combinations of thenormalized thickness Hs/λ of the SiO₂ film and Euler angle Θ when thenormalized thickness H/λ of the nickel or molybdenum electrode is about0.008 to about 0.06, about 0.017 to about 0.06, and about 0.023 to about0.06 are shown in Table 14. Euler angle Θ shown in Table 14 may vary byabout −2° to about +4° caused by a variation in the electrode fingerwidth or a variation in the single crystal substrate.

[0342] When manufacturing SAW apparatuses, although φ and ψ of the Eulerangles deviate from 0° by about ±3°, substantially the samecharacteristic as that when φ and ψ are 0° are obtained. TABLE 14 SiO₂thickness Euler angles of LiTaO₃ More preferable Hs/λ (°) Euler angles(°) 0.1-0.2 0 ± 3, 105-140, 0 ± 3 0 ± 3, 110-135, 0 ± 3 0.2-0.3 0 ± 3,105-140, 0 ± 3 0 ± 3, 108-135, 0 ± 3 0.3-0.4 0 ± 3, 104-139, 0 ± 3 0 ±3, 108-133, 0 ± 3

[0343] Optimal combinations of the normalized thickness Hs/λ of the SiO₂film and Euler angle Θ when the normalized thickness H/λ of the nickelelectrode is about 0.008 to about 0.06, about 0.02 to about 0.06, andabout 0.027 to about 0.06 shown in FIGS. 90 through 93 are shown inTable 15. TABLE 15 SiO₂ thickness Euler angles of More preferable Hs/λLiTaO₃ (°) Euler angles (°) 0.1-0.2 0 ± 3, 106-140, 0 ± 3 0 ± 3,110-135, 0 ± 3 0.2-0.3 0 ± 3, 105-137, 0 ± 3 0 ± 3, 108-134, 0 ± 30.3-0.4 0 ± 3, 104-133, 0 ± 3 0 ± 3, 108-132, 0 ± 3

[0344] Optimal combinations of the normalized thickness Hs/λ of the SiO₂film and Euler angle Θ when the normalized thickness H/λ of themolybdenum electrode is about 0.008 to about 0.06, about 0.017 to about0.06, and about 0.023 to about 0.06 shown in FIGS. 94 through 97 areshown in Table 16. TABLE 16 SiO₂ thickness Euler angles of Morepreferable Hs/λ LiTaO₃ (°) Euler angles (°) 0.1-0.2 0 ± 3, 107-141, 0 ±3 0 ± 3, 110-135, 0 ± 3 0.2-0.3 0 ± 3, 104-141, 0 ± 3 0 ± 3, 109-135, 0± 3 0.3-0.4 0 ± 3, 104-138, 0 ± 3 0 ± 3, 108-133, 0 ± 3

[0345] When the normalized thickness H/λ of the electrode made of ametal having the above-described density, Young's modulus, andtransversal-wave sonic wave is about 0.008 to about 0.06, about 0.017 toabout 0.06, and about 0.023 to about 0.06, as indicated in Table 14, thenormalized thickness Hs/λ of the SiO₂ film is preferably about 0.1 toabout 0.4 in order to set the range of the TCF to be between about −20ppm/° C. and about +20 ppm/° C. In this case, Euler angle Θ of theLiTaO₃ substrate is preferably between about 104° to about 140°(corresponding to the rotation angle of about 14° to about 50°), andmore preferably, the Euler angles shown on the right side of Table 14are selected according to the normalized thickness Hs/λ of the SiO₂film.

[0346] Similarly, when the normalized thickness H/λ of the nickelelectrode is about 0.008 to about 0.06, about 0.02 to about 0.06, andabout 0.027 to about 0.06, the normalized thickness Hs/λ of the SiO₂film is preferably about 0.1 to about 0.4 in order to set the range ofthe TCF to be between about −20 ppm/° C. and about +20 ppm/° C. In thiscase, Euler angle Θ of the LiTaO₃ substrate is preferably between about104° to about 140°, and more preferably, the Euler angles shown on theright side of Table 15 are selected according to the normalizedthickness Hs/λ of the SiO₂ film.

[0347] Similarly, when the normalized thickness H/λ of the molybdenumelectrode is about 0.008 to about 0.06, about 0.02 to about 0.06, andabout 0.027 to about 0.06, the thickness Hs/λ of the SiO₂ film ispreferably about 0.1 to about 0.4 in order to set the range of the TCFto be between about −20 ppm/° C. and about +20 ppm/° C. In this case,Euler angle Θ of the LiTaO₃ substrate preferably between about 104° toabout 141°, and more preferably, the Euler angles shown on the rightside of Table 16 are selected according to the normalized thickness ofthe SiO₂ film.

[0348] The Euler angles of LiTaO₃ shown in Table 14 through Table 16were selected so that the attenuation constant becomes about 0.1 orlower. The more preferable Euler angles shown in Table 14 through Table16 were selected so that the attenuation constant becomes about 0.05 orlower. The relationships between the Hs/λ of the SiO₂ film and the Eulerangles shown in Table 14 through Table 16 when the normalized thicknessH/λ of the electrode is from about 0.095, about 0.017, and about 0.023were determined in terms of the normalized thickness H/λ of the nickelor molybdenum electrode shown in FIGS. 90 through 97.

[0349] When manufacturing the SAW apparatus of this preferredembodiment, it is preferable that an IDT made of the above-describedspecific metal, such as nickel or molybdenum, is formed on a rotatedY-plate X-propagating LiTaO₃ substrate. Then, the frequency is adjusted.Then, a SiO₂ film having a thickness that can reduce the attenuationconstant α is formed. This is explained below with reference to FIGS. 98through 101. Nickel and molybdenum IDTs having different thicknessvalues and SiO₂ films having different thickness values were formed on arotated Y-plate X-propagating LiTaO₃ substrate (Euler angles (0°, 126°,0°)). FIGS. 98 and 100 illustrate a change in the acoustic velocity of aleaky SAW with respect to the thickness of the nickel electrode and thethickness of the molybdenum electrode, respectively. FIGS. 99 and 101illustrate a change in the acoustic velocity of a leaky SAW with respectto the thickness of the SiO₂ film. By comparing FIGS. 98 and 99, andFIGS. 100 and 101, it is seen that a change in the acoustic velocity ofthe SAW is much larger when the thickness of the electrode is variedthan when the thickness of the SiO₂ film is varied. Accordingly, it isdesirable that the frequency is adjusted before the formation of theSiO₂ film. It is desirable that the frequency is adjusted after a nickelor molybdenum IDT is formed by laser etching or ion etching.

[0350] In this embodiment, a 14°-50°-rotated Y-plate X-propagatingLiTaO₃ substrate having Euler angles (0°, 104°-140°, 0°), an IDT made ofa metal having the above-described density, the Young's modulus, and thetransversal-wave acoustic velocity, such as nickel or molybdenum, havinga normalized thickness H/λ of about 0.008 to about 0.06, and a SiO₂ filmhaving a normalized thickness Hs/λ of about 0.10 to about 0.40 arepreferably used. The number and the structure of IDTs are notparticularly restricted. That is, the present invention can be appliedto, not only the SAW apparatus shown in FIG. 15, but also various typesof SAW resonators and SAW filters as long as the above-describedconditions are satisfied.

[0351] While preferred embodiments of the invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the invention. The scope of the invention, therefore, is to bedetermined solely by the following claims.

What is claimed is:
 1. A surface acoustic wave apparatus comprising: apiezoelectric substrate including at least one of LiTaO₃ and LiNbO₃ andhaving an electromechanical coupling coefficient that is about 15% orgreater; at least one electrode provided on the piezoelectric substrateand including at least one of a metal having a density higher than Al,an alloy including a metal having a density higher than Al, and alaminated film including a metal having a density higher than Al or analloy including a metal having a density higher than Al; a firstinsulating layer provided on the piezoelectric substrate in an areaother than an area in which said at least one electrode is provided andhaving a thickness which substantially equals a thickness of said atleast one electrode; and a second insulating layer disposed on thepiezoelectric substrate to cover said at least one electrode and saidfirst insulating layer; wherein the density of said at least oneelectrode is about 1.5 times or greater than the density of said firstinsulating layer.
 2. A surface acoustic wave apparatus comprising: apiezoelectric substrate; at least one electrode provided on thepiezoelectric substrate and including one of a metal and an alloy; aprotective metal film provided on said at least one electrode andincluding a metal or an alloy having higher erosion-resistantcharacteristics than the metal or the alloy of the at least oneelectrode; a first insulating layer provided on the piezoelectricsubstrate in an area other than an area in which said at least oneelectrode is provided and having a thickness substantially equal to atotal thickness of said at least one electrode and said protective metalfilm; and a second insulating layer arranged to cover said protectivemetal film and said first insulating layer.
 3. A surface acoustic waveapparatus according to claim 2, wherein the average density of alaminated structure of said at least one electrode and said protectivemetal film is about 1.5 times or greater than a density of said firstinsulating layer.
 4. A surface acoustic wave apparatus according toclaim 1, wherein the said first and second insulating layers includeSiO₂.
 5. A surface acoustic wave apparatus according to claim 1, whereinsaid surface acoustic wave apparatus utilizes the reflection of asurface acoustic wave.
 6. A surface acoustic wave apparatus according toclaim 1, wherein: said piezoelectric substrate is a LiTaO₃ substratehaving Euler angles of about (0±3°, 104°-140°, 0±3°); said first andsecond insulating layers include a SiO₂ film; a normalized thicknessHs/λ ranges from about 0.03 to about 0.45 where Hs is a total thicknessof the SiO₂ film of said first and second insulating layers and λrepresents a wavelength of a surface acoustic wave; and a normalizedthickness H/λ of said at least one electrode satisfies the following:0.005≦H/λ≦0.00025×

²−0.01056×

+0.16473 where H indicates a thickness of said at least one electrode, λrepresents the wavelength of the surface acoustic wave, and

represents an average density of said at least one electrode.
 7. Asurface acoustic wave apparatus according to claim 1, wherein: saidpiezoelectric substrate is a LiTaO₃ substrate having Euler angles ofabout (0±3°, 115°-148°, 0±3°); said first and second insulating layersinclude a SiO₂ film; a normalized thickness Hs/λ ranges from about 0.03to about 0.45 where Hs is a total thickness of the SiO₂ film of saidfirst and second insulating layers and λ is a wavelength of a surfaceacoustic wave; the metal having a density higher than Al has a densityof about 15000 to about 23000 kg/m³, a Young's modulus of about 0.5×10¹¹to about 1.0×10¹¹ N/m², or a transversal-wave acoustic velocity of about1000 to about 2000 m/s; and a normalized thickness H/λ ranges from about0.013 to about 0.032 where H is a thickness of said at least oneelectrode and λ represents a wavelength of a surface acoustic wave.
 8. Asurface acoustic wave apparatus according to claim 7, wherein the metalhaving a density higher than Al is Au.
 9. A surface acoustic waveapparatus according to claim 7, wherein the Euler angles of thepiezoelectric LiTaO₃ substrate are about (0±3°, 132°-148°, 0±3°).
 10. Asurface acoustic wave apparatus according to claim 7, wherein Θ of theEuler angles of the piezoelectric LiTaO₃ substrate is between about 1150and about 132°.
 11. A surface acoustic wave apparatus according to claim7, wherein the Euler angles (0±3°, Θ, 0±3°) of the piezoelectric LiTaO₃substrate, the normalized thickness H/λ of said at least one electrode,and the normalized thickness Hs/λ of the SiO₂ film of said first andsecond insulating layers are approximately equal to one of the followingcombinations: θ of Euler angles Electrode SiO₂ film thickness (0 ± 3°,θ, 0 ± 3°) thickness (H/λ) (Hs/λ) 120.0° ≦ θ < 123.0° 0.013-0.0180.15-0.45 123.0° ≦ θ < 124.5° 0.013-0.022 0.10-0.40 124.5° ≦ θ < 125.5°0.013-0.025 0.07-0.40 125.5° ≦ θ < 127.5° 0.013-0.025 0.06-0.40 127.5° ≦θ < 129.0° 0.013-0.028 0.04-0.40 129.0° ≦ θ < 130.0° 0.017-0.0300.03-0.42 130.0° ≦ θ < 131.5° 0.017-0.030 0.03-0.42 131.5° ≦ θ < 133.0°0.018-0.028 0.05-0.33 133.0° ≦ θ < 135.0° 0.018-0.030 0.05-0.30 135.0° ≦θ < 137.0° 0.019-0.032 0.05-0.25 137.0° ≦ θ ≦ 140.0° 0.019-0.0320.05-0.25


12. A surface acoustic wave apparatus according to claim 7, wherein theEuler angles (0±3°, Θ, 0±3°) of the piezoelectric LiTaO₃ substrate, thenormalized thickness H/λ of said at least one electrode, and thenormalized thickness Hs/λ of the SiO₂ film of said first and secondinsulating layers are approximately equal to one of the followingcombinations: θ of Euler angles Electrode SiO₂ film (0 ± 3°, θ, 0 ± 3°)thickness (H/λ) thickness (Hs/λ) 129.0° ≦ θ < 130.0° 0.022-0.0280.04-0.40 130.0° ≦ θ < 131.5° 0.022-0.028 0.04-0.40 131.5° ≦ θ < 133.0°0.022-0.028 0.05-0.33 133.0° ≦ θ < 135.0° 0.022-0.030 0.05-0.30 135.0° ≦θ < 137.0° 0.022-0.032 0.05-0.25 137.0° ≦ θ ≦ 140.0° 0.022-0.0320.05-0.25


13. A surface acoustic wave apparatus according to claim 1, wherein:said piezoelectric substrate is a LiTaO₃ substrate having Euler anglesof about (0±3°, 113°-142°, 0±3°); said first and second insulatinglayers include a SiO₂ film; a normalized thickness Hs/λ ranges fromabout 0.10 to about 0.40 where Hs is a total thickness of the SiO₂ filmof said first and second insulating layers and λ is a wavelength of asurface acoustic wave; the metal having a density higher than Al has adensity of about 5000 to about 15000 kg/m³, a Young's modulus of about0.5×10¹¹ to about 1.0×10¹¹ N/m², or a transversal-wave acoustic velocityof about 1000 to about 2000 m/s; and the normalized thickness H/λ rangesfrom about 0.01 to about 0.08 where H is a thickness of said at leastone electrode.
 14. A surface acoustic wave apparatus according to claim13, wherein the metal having a density higher than Al is Ag.
 15. Asurface acoustic wave apparatus according to claim 13, wherein thenormalized thickness Hs/λ of the SiO₂ film of said first and secondinsulating layers and the Euler angles (Φ, Θ, Ψ) of the piezoelectricLiTaO₃ substrate are approximately equal to one of the followingcombinations: SiO₂ thickness Euler angles of (Hs/λ) LiTaO₃ (°) 0.15-0.180 ± 3, 117-137, 0 ± 3 0.18-0.23 0 ± 3, 117-136, 0 ± 3 0.23-0.28 0 ± 3,115-135, 0 ± 3 0.28-0.33 0 ± 3, 113-133, 0 ± 3 0.33-0.38 0 ± 3, 113-135,0 ± 3 0.38-0.40 0 ± 3, 113-132, 0 ± 3


16. A surface acoustic wave apparatus according to claim 13, wherein thenormalized thickness H/λ of said at least one electrode is about 0.02 toabout 0.06 and wherein the normalized thickness Hs/λ of the SiO₂ film ofsaid first and second insulating layers and the Euler angles (Φ, Θ, Ψ)of the piezoelectric LiTaO₃ substrate are approximately equal to one ofthe following combinations: SiO₂ thickness Euler angles of (Hs/λ) LiTaO₃(°) 0.15-0.18 0 ± 3, 120-133, 0 ± 3 0.18-0.23 0 ± 3, 120-137, 0 ± 30.23-0.28 0 ± 3, 120-135, 0 ± 3 0.28-0.33 0 ± 3, 118-135, 0 ± 30.33-0.38 0 ± 3, 115-133, 0 ± 3 0.38-0.40 0 ± 3, 113-130, 0 ± 3


17. A surface acoustic wave apparatus according to claim 13, wherein thenormalized thickness H/λ of said at least one electrode is about 0.03 toabout 0.05 and wherein the normalized thickness Hs/λ of the SiO₂ film ofsaid first and second insulating layers and the Euler angles (Φ, Θ, Ψ)of the piezoelectric LiTaO₃ substrate are approximately equal to one ofthe following combinations: SiO₂ thickness Euler angles of (Hs/λ) LiTaO₃(°) 0.15-0.18 0 ± 3, 122-142, 0 ± 3 0.18-0.23 0 ± 3, 120-140, 0 ± 30.23-0.28 0 ± 3, 117-138, 0 ± 3 0.28-0.33 0 ± 3, 116-136, 0 ± 30.33-0.38 0 ± 3, 114-135, 0 ± 3 0.38-0.40 0 ± 3, 113-130, 0 ± 3


18. A surface acoustic wave apparatus according to claim 1, wherein:said piezoelectric substrate is a LiTaO₃ substrate having Euler anglesof about (0±3°, 113°-137°, 0±3°); said first and second insulatinglayers include a SiO₂ film; the normalized thickness Hs/λ ranges fromabout 0.10 to about 0.40 where Hs is a total thickness of the SiO₂ filmof said first and second insulating layers and λ is a wavelength of asurface acoustic wave; the metal having a density higher than Al has adensity of about 5000 to about 15000 kg/m³, a Young's modulus of about1.0×10¹¹ to about 2.05×10¹¹ N/m², or a transversal-wave acousticvelocity of about 2000 to about 2800 m/s; and a normalized thickness H/λranges from about 0.01 to about 0.08 where H is a thickness of said atleast one electrode.
 19. A surface acoustic wave apparatus according toclaim 18, wherein the metal having a density higher than Al is Cu.
 20. Asurface acoustic wave apparatus according to claim 18, wherein thenormalized thickness Hs/λ of the SiO₂ film of said first and secondinsulating layers and the Euler angles (Φ, Θ, Φ) of the piezoelectricLiTaO₃ substrate are approximately equal to one of the followingcombinations: SiO₂ thickness Euler angles of (Hs/λ) LiTaO₃ (°) 0.15-0.180 ± 3, 117-137, 0 ± 3 0.18-0.23 0 ± 3, 117-136, 0 ± 3 0.23-0.28 0 ± 3,115-135, 0 ± 3 0.28-0.33 0 ± 3, 113-133, 0 ± 3 0.33-0.38 0 ± 3, 113-135,0 ± 3 0.38-0.40 0 ± 3, 113-132, 0 ± 3


21. A surface acoustic wave apparatus according to claim 18, wherein Θof the Euler angles (0±3°, Θ, 0±3°) is in a range defined by thefollowing expression: Θ_(min)−2°<Θ≦Θ_(min)+2° where Θ_(min) is a valueexpressed by one of the following equation when the normalized thicknessH/λ of said at least one electrode is in a range (a) through (e): (a)when 0<H/λ≦0.01 Θ_(min)=−139.713×Hs ³+43.07132×Hs²−20.568011×Hs+125.8314; (b) when 0.01<H/λ≦0.03 Θ_(min)=−139.660×Hs³+46.02985×Hs ²−21.141500×Hs+127.4181; (c) when 0.03<H/λ≦0.05Θ_(min)=−139.607×Hs ³+48.98838×Hs ²−21.714900×Hs+129.0048; (d) when0.05<H/λ≦0.07 Θ_(min)=−112.068×Hs ³+39.60355×Hs ²−21.186000×Hs+129.9397; and (e) when 0.07<H/λ≦0.09 Θ_(min)=−126.954×Hs³+67.40488×Hs ²−29.432000×Hs+131.5686.
 22. A surface acoustic waveapparatus according to claim 18, wherein the normalized thickness Hs/λof the SiO₂ film of said first and second insulating layers and theEuler angles (Φ, Θ, Ψ) of the piezoelectric LiTaO₃ substrate areapproximately equal to one of the followings combinations: SiO₂thickness Euler angles of (Hs/λ) LiTaO₃ (°) 0.15-0.18 0 ± 3, 117-125, 0± 3 0.18-0.23 0 ± 3, 117-125, 0 ± 3 0.23-0.28 0 ± 3, 115-125, 0 ± 30.28-0.33 0 ± 3, 113-125, 0 ± 3 0.33-0.38 0 ± 3, 113-125, 0 ± 30.38-0.40 0 ± 3, 113-125, 0 ± 3


23. A surface acoustic wave apparatus according to claim 1, wherein:said piezoelectric substrate is a LiTaO₃ substrate having Euler anglesof about (0±3°, 112°-138°, 0±3°); said first and second insulatinglayers include a SiO₂ film; a normalized thickness Hs/λ ranges fromabout 0.10 to about 0.40 where Hs is a total thickness of the SiO₂ filmof said first and second insulating layers and λ represents a wavelengthof a surface acoustic wave; the metal having a density higher than Alhas a density of about 15000 to about 23000 kg/m³, a Young's modulus ofabout 2.0×10¹¹ to about 4.5×10¹¹N/m², or a transversal-wave acousticvelocity of about 2800 to about 3500 m/s; and a normalized thickness H/λranges from about 0.0025 to about 0.06 where H indicates a thickness ofsaid at least one electrode.
 24. A surface acoustic wave apparatusaccording to claim 23, wherein the metal having a density higher than Alis tungsten.
 25. A surface acoustic wave apparatus according to claim23, wherein the normalized thickness H/λ of said at least one electrodeis about 0.012 to about 0.053.
 26. A surface acoustic wave apparatusaccording to claim 25, wherein the normalized thickness H/λ of said atleast one electrode is about 0.015 to about 0.042.
 27. A surfaceacoustic wave apparatus according to claim 23, wherein saidpiezoelectric substrate is a LiTaO₃ substrate having Euler angles ofabout (0±3°, 115°-135°, 0±3°).
 28. A surface acoustic wave apparatusaccording to claim 23, wherein the normalized thickness H/λ of said atleast one electrode is about 0.012 to about 0.053 and wherein thenormalized thickness Hs/λ of the SiO₂ film of said first and secondinsulating layers and the Euler angles (Φ, Θ, Ψ) of the piezoelectricLiTaO₃ substrate are approximately equal to one of the followingcombinations: SiO₂ thickness Euler angles of LiTaO₃ (Hs/λ) (°) 0.10-0.150 ± 3, 114.2-138.0, 0 ± 3 0.15-0.20 0 ± 3, 113.0-137.8, 0 ± 3 0.20-0.300 ± 3, 113.0-137.5, 0 ± 3 0.30-0.35 0 ± 3, 112.7-137.0, 0 ± 3 0.35-0.400 ± 3, 112.5-136.0, 0 ± 3


29. A surface acoustic wave apparatus according to claim 23, wherein thenormalized thickness H/λ of said at least one electrode is about 0.015to about 0.042 and wherein the normalized thickness Hs/λ of the SiO₂film of said first and second insulating layers and the Euler angles (Φ,Θ, Ψ) of the piezoelectric LiTaO₃ substrate are approximately equal toone of the following combinations: SiO₂ thickness Euler angles of LiTaO₃(Hs/λ) (°) 0.10-0.15 0 ± 3, 114.3-138.0, 0 ± 3 0.15-0.20 0 ± 3,113.0-137.5, 0 ± 3 0.20-0.30 0 ± 3, 112.5-137.0, 0 ± 3 0.30-0.35 0 ± 3,112.2-136.5, 0 ± 3 0.35-0.40 0 ± 3, 112.0-135.3, 0 ± 3


30. A surface acoustic wave apparatus according to claim 1, wherein:said piezoelectric substrate is a LiTaO₃ substrate having Euler anglesof about (0±3°, 104°-148°, 0±3°); said first and second insulatinglayers include a SiO₂ film; a normalized thickness Hs/λ ranges fromabout 0.10 to about 0.40 where Hs is a total thickness of the SiO₂ filmforming said first and second insulating layers and λ is a wavelength ofa surface acoustic wave; the metal having a density higher than Al has adensity of about 15000 to about 23000 kg/m³, a Young's modulus of about1.0×10¹¹ to about 2.0×10¹¹ N/m², or a transversal-wave acoustic velocityof about 2000 to about 2800 m/s; and a normalized thickness H/λ rangesfrom 0.004 to 0.055 where H is a thickness of said at least oneelectrode.
 31. A surface acoustic wave apparatus according to claim 30,wherein the metal having a density higher than Al is tantalum.
 32. Asurface acoustic wave apparatus according to claim 30, wherein thenormalized thickness H/λ of said at least one electrode is about 0.01 toabout 0.055.
 33. A surface acoustic wave apparatus according to claim30, wherein the normalized thickness H/λ of said at least one electrodeis about 0.016 to about 0.045.
 34. A surface acoustic wave apparatusaccording to claim 30, wherein said piezoelectric substrate is a LiTaO₃substrate having Euler angles of about (0±3°, 111°-143°, 0±3°).
 35. Asurface acoustic wave apparatus according to claim 30, wherein thenormalized thickness H/λ of said at least one electrode is about 0.01 toabout 0.055 and wherein the normalized thickness Hs/λ of the SiO₂ filmof said first and second insulating layers and the Euler angles (Φ, Θ,Ψ) of the piezoelectric LiTaO₃ substrate are approximately equal to oneof the following combinations: SiO₂ thickness Euler angles of LiTaO₃(Hs/λ) (°) 0.10-0.15 0 ± 3, 110.5-148.0, 0 ± 3 0.15-0.20 0 ± 3,108.0-147.5, 0 ± 3 0.20-0.30 0 ± 3, 105.0-148.0, 0 ± 3 0.30-0.35 0 ± 3,104.5-148.0, 0 ± 3 0.35-0.40 0 ± 3, 104.0-145.0, 0 ± 3


36. A surface acoustic wave apparatus according to claim 30, wherein thenormalized thickness H/λ of said at least one electrode is about 0.016to about 0.045 and wherein the normalized thickness Hs/, of the SiO₂film of said first and second insulating layers and the Euler angles (Φ,Θ, Ψ) of the piezoelectric LiTaO₃ substrate are approximately equal toone of the following combinations: SiO₂ thickness Euler angles of LiTaO₃(Hs/λ) (°) 0.10-0.15 0 ± 3, 113.0-144.0, 0 ± 3 0.15-0.20 0 ± 3,111.0-144.0, 0 ± 3 0.20-0.30 0 ± 3, 108.0-144.0, 0 ± 3 0.30-0.35 0 ± 3,107.5-143.0, 0 ± 3 0.35-0.40 0 ± 3, 107.0-140.5, 0 ± 3


37. A surface acoustic wave apparatus according to claim 1, wherein:said piezoelectric substrate is a LiTaO₃ substrate having Euler anglesof about (0±3°, 90°-169°, 0±3°); said first and second insulating layersinclude a SiO₂ film; a normalized thickness Hs/λ ranges from about 0.10to about 0.40 where Hs is a total thickness of the SiO₂ film of saidfirst and second insulating layers and λ is a wavelength of a surfaceacoustic wave; the metal having a density higher than Al has a densityof about 15000 to about 23000 kg/m³, a Young's modulus of about 1.0×10¹¹to about 2.0×10¹¹ N/m², or a transversal-wave acoustic velocity of about1000 to about 2000 m/s; and a normalized thickness H/λ ranges from about0.005 to about 0.054 where H indicates a thickness of said at least oneelectrode.
 38. A surface acoustic wave apparatus according to claim 37,wherein the metal having a density higher than Al is platinum.
 39. Asurface acoustic wave apparatus according to claim 37, wherein saidpiezoelectric substrate is a LiTaO₃ substrate having Euler angles ofabout (0±3°, 90°-155°, 0±3°) and the normalized thickness H/λ of said atleast one electrode is about 0.01 to about 0.04.
 40. A surface acousticwave apparatus according to claim 39, wherein the normalized thicknessHs/λ of the SiO₂ film of said first and second insulating layers and theEuler angles (Φ, Θ, Ψ) of the piezoelectric LiTaO₃ substrate areapproximately equal to one of the following combinations: SiO₂ thicknessEuler angles of (Hs/λ) LiTaO₃ (°) 0.10 ≦ Hs/λ < 0.15 0 ± 3, 90-169, 0 ±3 0.15 ≦ Hs/λ < 0.20 0 ± 3, 90-167, 0 ± 3 0.20 ≦ Hs/λ < 0.25 0 ± 3,90-167, 0 ± 3 0.25 ≦ Hs/λ < 0.30 0 ± 3, 90-164, 0 ± 3 0.30 ≦ Hs/λ < 0.400 ± 3, 90-163, 0 ± 3


41. A surface acoustic wave apparatus according to claim 37, whereinsaid piezoelectric substrate is a LiTaO₃ substrate having Euler anglesabout (0±3°, 102°-150°, 0±3°) and the normalized thickness H/λ of saidat least one electrode is about 0.013 to about 0.033.
 42. A surfaceacoustic wave apparatus according to claim 41 wherein the normalizedthickness Hs/λ of the SiO₂ film of said first and second insulatinglayers and the Euler angles (Φ, Θ, Ψ) of the piezoelectric LiTaO₃substrate are approximately equal to one of the following combinations:SiO₂ thickness Euler angles of (Hs/λ) LiTaO₃ (°) 0.10 ≦ Hs/λ < 0.15 0 ±3, 106-155, 0 ± 3 0.15 ≦ Hs/λ < 0.20 0 ± 3, 104-155, 0 ± 3 0.20 ≦ Hs/λ <0.25 0 ± 3, 102-155, 0 ± 3 0.25 ≦ Hs/λ < 0.30 0 ± 3, 102-154, 0 ± 3 0.30≦ Hs/λ < 0.40 0 ± 3, 102-153, 0 ± 3


43. A surface acoustic wave apparatus according to claim 1, wherein:said piezoelectric substrate is a LiTaO₃ substrate having Euler anglesof about (0±3°, 104°-150°, 0±3°); said first and second insulatinglayers includes a SiO₂ film; a normalized thickness Hs/λ ranges from0.10 to 0.40 where Hs is a total thickness of the SiO₂ film of saidfirst and second insulating layers and λ is a wavelength of a surfaceacoustic wave; the metal having a density higher than Al has a densityof about 5000 to about 15000 kg/m³, a Young's modulus of about 2.0×10¹¹to about 4.5×10¹¹ N/m², or a transversal-wave acoustic velocity of about2800 to about 3500 m/s; and a normalized thickness H/λ ranges from about0.008 to about 0.06 where H is a thickness of said at least oneelectrode.
 44. A surface acoustic wave apparatus according to claim 43,wherein the metal having a density higher than Al is Ni.
 45. A surfaceacoustic wave apparatus according to claim 44, wherein the normalizedthickness H/λ of said at least one electrode is about 0.02 to about0.06.
 46. A surface acoustic wave apparatus according to claim 44,wherein the normalized thickness H/λ of said at least one electrode isabout 0.027 to about 0.06.
 47. A surface acoustic wave apparatusaccording to claim 44, wherein the normalized thickness Hs/λ of the SiO₂film of said first and second insulating layers and the Euler angles (Φ,Θ, Ψ) of the piezoelectric LiTaO₃ substrate are approximately equal toone of the following combinations: SiO₂ thickness Euler angles of LiTaO₃(Hs/λ) (°) 0.1-0.2 0 ± 3, 106-140, 0 ± 3 0.2-0.3 0 ± 3, 105-137, 0 ± 30.3-0.4 0 ± 3, 104-133, 0 ± 3


48. A surface acoustic wave apparatus according to claim 43, wherein themetal having a density higher than Al is Mo.
 49. A surface acoustic waveapparatus according to claim 48, wherein the normalized thickness H/λ ofsaid at least one electrode is about 0.017 to about 0.06.
 50. A surfaceacoustic wave apparatus according to claim 48, wherein the normalizedthickness H/λ of said at least one electrode is about 0.023 to about0.06.
 51. A surface acoustic wave apparatus according to claim 48,wherein the normalized thickness Hs/λ of the SiO₂ film of said first andsecond insulating layers and the Euler angles (Φ, Θ, Ψ) of thepiezoelectric LiTaO₃ substrate are approximately equal to one of thefollowing combinations: SiO₂ thickness Euler angles of LiTaO₃ (Hs/λ) (°)0.1-0.2 0 ± 3, 107-141, 0 ± 3 0.2-0.3 0 ± 3, 104-141, 0 ± 3 0.3-0.4 0 ±3, 104-138, 0 ± 3


52. A surface acoustic wave apparatus according to claim 1, wherein saidat least one electrode includes a laminated film including an electrodelayer made of a metal having a density higher than Al or an alloy havinga density higher than Al and at least one electrode layer made ofanother metal having an average density

determined by the following expression:

×0.7≦

≦

0×1.3 wherein

0 is the density of the metal having a density higher than Al.
 53. Asurface acoustic wave apparatus according to claim 1, wherein athickness of said second insulating layer is about 30% or smaller of athickness of said at least one electrode.
 54. A surface acoustic waveapparatus according to claim 1, wherein a leaky surface acoustic wave isused.
 55. A manufacturing method for a surface acoustic wave apparatus,comprising the steps of: preparing a piezoelectric substrate; forming afirst insulating layer on the entirety of one surface of thepiezoelectric substrate; removing, by using a resist pattern for formingan electrode pattern including at least one electrode, at least aportion of the first insulating layer in an area in which said at leastone electrode is to be formed, and; maintaining a laminated structure ofthe first insulating layer and the resist pattern in an area other thanthe area in which said at least one electrode is to be formed; formingsaid at least one electrode by forming an electrode film including atleast one of a metal having a density higher than Al and an alloyincluding a metal having a density higher than Al in an area of theportion of the first insulating layer which was removed and which has athickness substantially equal to a thickness of the first insulatinglayer; removing the resist pattern on the first insulating layer; andforming a second insulating layer to cover the first insulating layerand said at least one electrode.
 56. A manufacturing method according toclaim 55, wherein a density of the metal or the alloy of said at leastone electrode is about 1.5 times or greater than a density of the firstinsulating layer.
 57. A manufacturing method for a surface acoustic waveapparatus, comprising the steps of: preparing a piezoelectric substrate;forming a first insulating layer on the entirety of one surface of thepiezoelectric substrate; removing, by using a resist pattern for formingat least one electrode, a portion of the first insulating layer in anarea in which said at least one electrode is to be formed; maintaining alaminated structure of the first insulating layer and the resist patternin an area other than the area in which said at least one electrode isto be formed; forming said at least one electrode by forming a metal oran alloy in the area of the portion of the first insulating layer whichwas removed; forming, after the formation of said at least oneelectrode, a protective metal film made of a metal or an alloy havinghigher erosion-resistant characteristics than the metal or the alloy ofsaid at least one electrode on the entire surface of said at least oneelectrode such that a thickness of the protective metal film issubstantially equal to a thickness of the first insulating layer;removing the resist pattern on the first insulating layer and theprotective metal film laminated on the resist pattern; and forming asecond insulating layer to cover the protective metal film formed onsaid at least one electrode and the first insulating layer.
 58. Amanufacturing method according to claim 57, wherein the metal or thealloy of said at least one electrode and the metal or the alloy of theprotective metal film are selected such that the average density of thelaminated structure of said at least one electrode and the protectivemetal film is about 1.5 times or greater than the density of the firstinsulating layer.
 59. A manufacturing method for a surface acoustic waveapparatus, comprising the steps of: preparing a piezoelectric substrate;forming an electrode on the piezoelectric substrate; forming aninsulating layer to cover the electrode; and planarizing a difference ofthe height of the insulating layer between a portion where the electrodeis present and a portion where the electrode is not present.
 60. Amanufacturing method according to claim 59, wherein the planarizing stepis performed by an etch back process, a reverse sputtering process, or apolishing process.
 61. A manufacturing method according to claim 55,wherein the metal of said at least one electrode is selected from thegroup consisting of Au, Cu, Ag, W, Ta, Pt, Ni, Mo, the alloy primarilyincludes at least two metals from the group consisting of Au, Cu, Ag, W,Ta, Pt, Ni, Mo, and the first and second insulating layers include alayer of SiO₂.